Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
220 PM EDT Wed Apr 17 2024

Valid 00Z Thu Apr 18 2024 - 00Z Sat Apr 20 2024

...Severe weather and isolated flash flooding for the Great Lakes/Ohio
Valley this evening; threat shifts to the Ohio and middle Mississippi
valleys and Southern Plains Thursday...

...Warm to hot temperatures across the southern U.S.; chillier weather
spreading southeast from the northern Rockies/Plains...

Showers and thunderstorms will continue to develop into the evening along
and ahead of a cold front now advancing eastward across Lower Michigan and
the Ohio Valley. Some of these storms may become strong to severe,
producing damaging winds, large hail, and a few tornadoes. In addition to
severe weather, locally heavy rainfall and isolated flash flooding are
concerns as well.

Later this evening, storms are forecast to develop from the central Plains
into the lower Missouri Valley. These storms too may become strong to
severe, with damaging hail expected to be the primary threat.

As the system in Plains moves further east, storms are likely to redevelop
from the Ohio Valley into the southern Plains on Thursday. Severe weather
will once again become a concern, especially across portions of the mid
Mississippi into the lower Ohio valleys. The Storm Prediction Center has
issued an Enhanced Risk (level 3/5) for portions of the region, noting
that strong to severe storms capable of damaging winds, and possibly a few
tornadoes, are likely tomorrow. While widespread heavy rains are not
expected, locally heavy accumulations resulting in isolated flash flooding
are possible.

Temperatures across the southern U.S. will remain warm through the period,
with highs in the upper 80s and 90s common from the Southwest to the
Southeast over the next couple of days. Much cooler temperatures now
centered over the northern Rockies and Plains will spread southeastward,
lowering temperatures across much of the Midwest and Ohio Valley by Friday.

Pereira

Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Tue Apr 16 2024

Valid 12Z Fri Apr 19 2024 - 12Z Tue Apr 23 2024


...Overview...

The pattern during the medium range period should transition
towards more progressive flow after the start of the period on
Friday, as an Omega block over the northeast Pacific into western
North America and the northern U.S. tier begins to break down. A
cold front through the East late this week will be accompanied by
some showers and thunderstorms, with the Northeast drying out
thereafter. From the Southern Plains into the Southeast, a slow
moving cold front and shortwave energy will increase the heavy
rainfall potential, particularly across much of Texas on Saturday.
Into next week, fairly low amplitude troughing will be present
across both the West and East coasts, with upper ridging in
between, and generally fairly quiet conditions across the CONUS.


...Guidance/Predictability Assessment...

Latest guidance shows good agreement Friday and Saturday as an
upper low shifts into southeast Canada, bringing low amplitude
troughing to the northeastern U.S., while energy out of a deep low
in the Gulf of Alaska shifts through the eastern Pacific toward the
Northwest. By Sunday, there remains quite a bit of variability on
the strength and timing of the western energy as it moves inland
and towards the Northern Plains. GFS runs have consistently been on
the weaker side with this shortwave while CMC and ECMWF runs are a
bit deeper and slower (though the 00Z and new 12Z ECMWF runs are
faster than the slow outlier of the 12Z 4/15 run). Considering
typical model biases, generally preferred the non- NCEP models
though balanced somewhat with the GEFS mean for a middle ground.
After this, there are some differences in the details of energy
rounding the base of the Eastern U.S. trough, and even greater
uncertainty by Monday-Tuesday with another trough moving towards
the West Coast.

The WPC forecast today used a blend of the deterministic models
for Days 3-4. Gradually transitioned toward using more GEFS and
NAEFS ensemble means through the period to 60 percent by day 7. The
EC ensemble mean could not be used due to ongoing data issues but
it looked to be in good alignment. This maintained good continuity
with the overnight forecast.


...Weather/Hazards Highlights...

A cold front moving through the Northeast Friday-Saturday will be
accompanied by some generally light precipitation and storms, with
the southern portion slower to move or possibly stalling briefly
into the weekend across the Southern Plains-Southeast region.
Anomalous moisture and instability present in the vicinity of the
wavy front favors a low-end Marginal Risk area on Friday for parts
of the southern Plains and Mississippi Valley. This overall area
may have some potential for storm training with higher rain rate
potential, though guidance signals do not show great coherence for
details yet. Also most of this area has been rather dry as of late,
which should inhibit the overall flash flood threat, so the
Marginal is pretty borderline. Favorable flow into the Central
Rockies should work to enhance precipitation there too, with some
snow in the higher elevations at least. By the weekend, weak
shortwave energy reaching into the Southern Plains should help to
further enhance precipitation across Texas and vicinity on Saturday
with increasing heavy rain potential. Model guidance overall has
trended toward a southwest shift with the heavy rain, and thus have
shifted/expanded the Slight Risk toward this trend. The area
covers west-central Texas eastward toward Texarkana with a broader
surrounding Marginal. The front should progress and lay flatter
across the Southeast on Sunday and bring some rain there before
shifting mostly offshore for the workweek. Meanwhile some light to
locally moderate precipitation could come into the Northwest on
Saturday and shift across the northern tier early next week but
with considerable uncertainty.

By Friday and beyond, much of the Northeast should gradually cool
behind a cold front. Meanwhile, the upper trough over the northern
tier states and eventually into the East will support below normal
temperatures (with greater anomalies for highs than lows) for most
east of the Rockies but Florida by next weekend. Above normal
temperatures across the Southwest should gradually expand northward
underneath a building Western U.S. ridge and progress eastward
into the Rockies early next week. Northern parts of the West may
stay near normal due to the upper shortwave/cold front crossing the
region this weekend.


Tate/Santorelli


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
317 AM EDT Tue Apr 16 2024

Valid 00Z Wed Apr 17 2024 - 00Z Wed Apr 24 2024

The next week over Hawaii should be pretty quiet as surface high
pressure becomes established again north of the state. This should
support easterly trade winds and showers favoring the typical
windward locations. A weak system north of the islands around next
weekend may briefly disrupt trades, but will not have much if any
precipitation associated with it given below normal precipitable
water values. Surface high pressure will strengthen
north/northeast of Hawaii early next week bringing stronger and
breezy winds across Hawaii.

Santorelli

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
824 PM EDT Wed Apr 17 2024
Day 1
Valid 01Z Thu Apr 18 2024 - 12Z Thu Apr 18 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE GREAT LAKES, OHIO VALLEY AND WESTERN PARTS OF THE NORTHEAST...

...01Z Excessive Rainfall Outlook...

Progression of the cold front has allowed the removal of Michigan
and much of Ohio from the Marginal Risk area. The threat of
excessive rainfall remained over far eastern Ohio into parts of
adjoining states where the low/mid level flow continues to draw
moisture ahead of the approaching cold front. In the immediate
term...the concern is greatest where the southern part of a line
is becoming aligned with the mean low-level flow setting up the
possibility of cells training. Part of the convective line farther
north was more progressive but poised to move over areas that were
soaked with very heavy rain recently...so there is at least a low-
end threat into the overnight hours. Some convection over
northeast Mexico may make it across the international border into
parts of the middle Rio Grande Valley in Texas during the evening...but
the 18/00Z sounding from Del Rio showed an atmosphere that was
largely capped atmosphere...an idea that the HRRR has been
suggesting for a few runs and which should preclude much of an
excessive rainfall threat.

Bann


...16Z Update...

Minor adjustments were made to the southern edge of the previous
MRGL issuance across the Ohio Valley into the Mid Atlantic. This
was in conjunction with the latest trends in hi-res deterministic
and the QPF footprint within the NBM. Mid-level shortwave will
rotate around the base of the closed 5H reflection over the Great
Lakes and propagate eastward over northern IL/IN/OH before pivoting
across PA by the end of the forecast cycle. Locally heavy rainfall
from progressive convection will allow for flash flood concerns
within that area bordering Lake Erie down to about I-70 where the
best forcing will occur. This will cross over an area of lower FFGs
due to recent rainfall events causing antecedent conditions to be
primed for easier exceedance thresholds. The area of focus will be
over northeast OH into western PA where even 1 and 3-hour FFG
markers are hovering around that 1-1.5" range which is very low
and a possibility within today's setup. 12z HREF EAS probability
field is between 20-40% for exceeding 1" total rainfall between
Cleveland to Erie, aligned well with the ML algorithms from both
the GFS and ECMWF for the targeted location for best chance of
impact. As a result, did not feel there was a need to adjust the
northern extent of the risk area as it solidifies the forecast and
maintains continuity.

Across the Deep South, conditions have been fairly tame with
regards to the previously highlighted area. 12z CAMs remained "hot"
with the QPF interpretation, but radar and observational trends
negate the former runs and the newer hourly guidance is more in-
line with what is occurring which would be well below any chance of
a MRGL risk issuance. Will continue to monitor, but the threat of
flash flooding is trending closer to 0% than it is to the bottom of
the Marginal Risk threshold (5%).

Kleebauer

...Previous Discussion...

Showers and thunderstorms tracking across the Ohio Valley may
produce periods of heavy rainfall. Much of eastern Ohio and western
Pennsylvania have Low FFG which does maintain an elevated threat
for excessive rainfall and local flooding concerns. Model consensus
has accumulations less than 2 inches across this area. Multiple
rounds of convection will track through eastern portions of
Pennsylvania and into New Jersey could reach 1 inch within areas of
low FFG indices, especially in the 3 and 6-hr FFG intervals. The
Marginal Risk area that was already in effect was maintained for
this period.


Campbell/Kleebauer

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
824 PM EDT Wed Apr 17 2024
Day 2
Valid 12Z Thu Apr 18 2024 - 12Z Fri Apr 19 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS AND MISSISSIPPI VALLEY...

...20Z Update...

Marginal Risk area was expanded to the northeast to include more of
the Ohio Valley as latest guidance trends more bullish with the
prospects of greater convective coverage in-of eastern MO, southern
IL, and western KY. Latest probabilities for at least 1" and 2"/hr
rates have ramped up to 40-60% and 10-20% respectively across the
Mid-Mississippi Valley with the secondary pulse of heavier rates
located within central TX. Regional instability is highest across
the southern plains, but the combination of stronger mid-level
forcing along with sufficient buoyancy is located over the Mid-
Mississippi Valley where the best prospect for flooding is
anticipated. Overall, the primary synoptic and mesoscale pattern
are unchanged with only deviations anticipated in the general
convective placement within the MRGL risk area. Relative
progressive nature of the cold front will limit higher end
potential over the Missouri Basin, but an upgrade to a Slight is
not completely out of the question, pending evolution and trends
upstream as the shortwave exits out of Nebraska.

Kleebauer

...Previous Discussion...

A surface low pressure system and associated front will develop
across the Central Plains and advance toward the Mid-Mississippi
Valley and convection will fire off as the moist return flow from
the Gulf of Mexico drawls northward into the system. Locally heavy
rain will setup over Missouri and points southwest to central
Texas. The better concentration of the heavy rain will focus across
Missouri and surrounding locations. Recent rains have lowered some
of the FFG across this region and may have an increased
sensitivity to additional rain/heavy rain. A Marginal Risk area
covers part of northeast Texas to southern Missouri and western
Kentucky.

Campbell

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
824 PM EDT Wed Apr 17 2024
Day 3
Valid 12Z Fri Apr 19 2024 - 12Z Sat Apr 20 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE TEXAS BIG BEND AND WEST TEXAS...

...20Z Update...

The low pressure system will continue to have its associated
frontal boundary draped across the Midwest and Plains during
period while dryline sets up from the Oklahoma Panhandle to the Big
Bend area. Convection is expected to be along and south of the
front over the Southern/Central Plains and Lower Mississippi Valley
with the higher QPF near/east of the dryline in west-central
Texas. The consensus for the area over the Texas Big Bend up
through the Edwards Plateau has grown within this suite of
guidance with the environment primed for higher end convective
development from the Lower Trans Pecos, eastward into the Rio
Grande and adjacent Edwards Plateau. Ensemble probabilities remain
on the lower end, however they are within the 10-20% range for
totals exceeding 2" which would be sufficient for localized flood
concerns within the terrain focused over the area. Further
northeast into the Red River and southern OK, there's some
differences in timing of the approach of the front into that area
with the convergence pattern expected towards the back end of the
forecast period with a higher potential for flash flooding in the
successive D4 time frame. As a result, have removed the MRGL, for
now and will monitor any trends over the next series of numerical
guidance output. As we intake more hi-res deterministic data in the
following 48 hours, a secondary MRGL is possible for the Red River
basin with a gap in-between as probabilities for any appreciable
convective coverage is low between the Concho Valley into north TX.
A Marginal Risk area spans the Big Bend area northeast into the
Edwards Plateau and Concho Valley.


Campbell/Kleebauer

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Tue Apr 16 2024


A cold front moving through the Northeast Friday-Saturday will be
accompanied by some generally light precipitation and storms, with
the southern portion slower to move or possibly stalling briefly
into the weekend across the Southern Plains-Southeast region.
Anomalous moisture and instability present in the vicinity of the
wavy front favors a low-end Marginal Risk area on Friday for parts
of the southern Plains and Mississippi Valley. This overall area
may have some potential for storm training with higher rain rate
potential, though guidance signals do not show great coherence for
details yet. Also most of this area has been rather dry as of late,
which should inhibit the overall flash flood threat, so the
Marginal is pretty borderline. Favorable flow into the Central
Rockies should work to enhance precipitation there too, with some
snow in the higher elevations at least. By the weekend, weak
shortwave energy reaching into the Southern Plains should help to
further enhance precipitation across Texas and vicinity on Saturday
with increasing heavy rain potential. Model guidance overall has
trended toward a southwest shift with the heavy rain, and thus have
shifted/expanded the Slight Risk toward this trend. The area
covers west-central Texas eastward toward Texarkana with a broader
surrounding Marginal. The front should progress and lay flatter
across the Southeast on Sunday and bring some rain there before
shifting mostly offshore for the workweek. Meanwhile some light to
locally moderate precipitation could come into the Northwest on
Saturday and shift across the northern tier early next week but
with considerable uncertainty.

By Friday and beyond, much of the Northeast should gradually cool
behind a cold front. Meanwhile, the upper trough over the northern
tier states and eventually into the East will support below normal
temperatures (with greater anomalies for highs than lows) for most
east of the Rockies but Florida by next weekend. Above normal
temperatures across the Southwest should gradually expand northward
underneath a building Western U.S. ridge and progress eastward
into the Rockies early next week. Northern parts of the West may
stay near normal due to the upper shortwave/cold front crossing the
region this weekend.


Tate/Santorelli

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Tue Apr 16 2024


A cold front moving through the Northeast Friday-Saturday will be
accompanied by some generally light precipitation and storms, with
the southern portion slower to move or possibly stalling briefly
into the weekend across the Southern Plains-Southeast region.
Anomalous moisture and instability present in the vicinity of the
wavy front favors a low-end Marginal Risk area on Friday for parts
of the southern Plains and Mississippi Valley. This overall area
may have some potential for storm training with higher rain rate
potential, though guidance signals do not show great coherence for
details yet. Also most of this area has been rather dry as of late,
which should inhibit the overall flash flood threat, so the
Marginal is pretty borderline. Favorable flow into the Central
Rockies should work to enhance precipitation there too, with some
snow in the higher elevations at least. By the weekend, weak
shortwave energy reaching into the Southern Plains should help to
further enhance precipitation across Texas and vicinity on Saturday
with increasing heavy rain potential. Model guidance overall has
trended toward a southwest shift with the heavy rain, and thus have
shifted/expanded the Slight Risk toward this trend. The area
covers west-central Texas eastward toward Texarkana with a broader
surrounding Marginal. The front should progress and lay flatter
across the Southeast on Sunday and bring some rain there before
shifting mostly offshore for the workweek. Meanwhile some light to
locally moderate precipitation could come into the Northwest on
Saturday and shift across the northern tier early next week but
with considerable uncertainty.

By Friday and beyond, much of the Northeast should gradually cool
behind a cold front. Meanwhile, the upper trough over the northern
tier states and eventually into the East will support below normal
temperatures (with greater anomalies for highs than lows) for most
east of the Rockies but Florida by next weekend. Above normal
temperatures across the Southwest should gradually expand northward
underneath a building Western U.S. ridge and progress eastward
into the Rockies early next week. Northern parts of the West may
stay near normal due to the upper shortwave/cold front crossing the
region this weekend.


Tate/Santorelli

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
221 PM EDT Tue Apr 16 2024

Valid 00Z Wed Apr 17 2024 - 00Z Sat Apr 20 2024


...Northern Rockies...
Day 1...

A vigorous positively-tilted trough digs southeastward across the
northern Rockies tonight into Wednesday. Post-cold frontal upslope
on surface northerly flow and the left-exit region of a 110kt NWly
jet will further add lift across MT, ID, and northern WY. Thus,
expect a period of generally light to moderate snow from Glacier NP
southeast through Yellowstone to the Bighorns. The Big Horn
Mountains are likely to be the recipients of the most snow from
this system, with multiple feet of snow expected. Around
Yellowstone, expect 1-2 feet through Thursday, while elsewhere
amounts should stay under 6 inches. By Wednesday night the trough
will push east, moving these same areas into the left-entrance
region of the jet with the supporting shortwave out over the
northern Plains. This should rapidly weaken any ongoing snow in the
aforementioned areas.

...Rest of the Continental US...

Some minor lake-effect snow off of Lake Superior is possible over
portions of the U.P. of Michigan just beyond the Day 3 time period
Friday night.

The probability of significant icing is less than 10 percent.

Wegman

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Tue Apr 16 2024

Valid 12Z Fri Apr 19 2024 - 12Z Tue Apr 23 2024


...Overview...

The pattern during the medium range period should transition
towards more progressive flow after the start of the period on
Friday, as an Omega block over the northeast Pacific into western
North America and the northern U.S. tier begins to break down. A
cold front through the East late this week will be accompanied by
some showers and thunderstorms, with the Northeast drying out
thereafter. From the Southern Plains into the Southeast, a slow
moving cold front and shortwave energy will increase the heavy
rainfall potential, particularly across much of Texas on Saturday.
Into next week, fairly low amplitude troughing will be present
across both the West and East coasts, with upper ridging in
between, and generally fairly quiet conditions across the CONUS.


...Guidance/Predictability Assessment...

Latest guidance shows good agreement Friday and Saturday as an
upper low shifts into southeast Canada, bringing low amplitude
troughing to the northeastern U.S., while energy out of a deep low
in the Gulf of Alaska shifts through the eastern Pacific toward the
Northwest. By Sunday, there remains quite a bit of variability on
the strength and timing of the western energy as it moves inland
and towards the Northern Plains. GFS runs have consistently been on
the weaker side with this shortwave while CMC and ECMWF runs are a
bit deeper and slower (though the 00Z and new 12Z ECMWF runs are
faster than the slow outlier of the 12Z 4/15 run). Considering
typical model biases, generally preferred the non- NCEP models
though balanced somewhat with the GEFS mean for a middle ground.
After this, there are some differences in the details of energy
rounding the base of the Eastern U.S. trough, and even greater
uncertainty by Monday-Tuesday with another trough moving towards
the West Coast.

The WPC forecast today used a blend of the deterministic models
for Days 3-4. Gradually transitioned toward using more GEFS and
NAEFS ensemble means through the period to 60 percent by day 7. The
EC ensemble mean could not be used due to ongoing data issues but
it looked to be in good alignment. This maintained good continuity
with the overnight forecast.


...Weather/Hazards Highlights...

A cold front moving through the Northeast Friday-Saturday will be
accompanied by some generally light precipitation and storms, with
the southern portion slower to move or possibly stalling briefly
into the weekend across the Southern Plains-Southeast region.
Anomalous moisture and instability present in the vicinity of the
wavy front favors a low-end Marginal Risk area on Friday for parts
of the southern Plains and Mississippi Valley. This overall area
may have some potential for storm training with higher rain rate
potential, though guidance signals do not show great coherence for
details yet. Also most of this area has been rather dry as of late,
which should inhibit the overall flash flood threat, so the
Marginal is pretty borderline. Favorable flow into the Central
Rockies should work to enhance precipitation there too, with some
snow in the higher elevations at least. By the weekend, weak
shortwave energy reaching into the Southern Plains should help to
further enhance precipitation across Texas and vicinity on Saturday
with increasing heavy rain potential. Model guidance overall has
trended toward a southwest shift with the heavy rain, and thus have
shifted/expanded the Slight Risk toward this trend. The area
covers west-central Texas eastward toward Texarkana with a broader
surrounding Marginal. The front should progress and lay flatter
across the Southeast on Sunday and bring some rain there before
shifting mostly offshore for the workweek. Meanwhile some light to
locally moderate precipitation could come into the Northwest on
Saturday and shift across the northern tier early next week but
with considerable uncertainty.

By Friday and beyond, much of the Northeast should gradually cool
behind a cold front. Meanwhile, the upper trough over the northern
tier states and eventually into the East will support below normal
temperatures (with greater anomalies for highs than lows) for most
east of the Rockies but Florida by next weekend. Above normal
temperatures across the Southwest should gradually expand northward
underneath a building Western U.S. ridge and progress eastward
into the Rockies early next week. Northern parts of the West may
stay near normal due to the upper shortwave/cold front crossing the
region this weekend.


Tate/Santorelli


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw