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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1603Z Sep 19, 2019)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1203 PM EDT Thu Sep 19 2019

Valid 12Z Sun Sep 22 2019 - 12Z Thu Sep 26 2019

...Heavy rainfall threats in the Mid-MS Valley/Midwest as well as
the Southwest Sun/Mon...


...Overview...

Amplified pattern will only slowly transition toward more zonal
flow by the end of next week as multiple tropical systems traverse
the Atlantic and Pacific waters. Two troughs in the Pacific
Northwest and Plains will be significant players for the rainfall
early in the medium range period (Sun/Mon) as each will tap
tropical moisture due to Mario/Lorena in the East Pacific and
leftover moisture from Imelda in the Mid-Mississippi Valley. The
pattern will tend to favor broad troughing by next Thursday across
the northern tier as an upper low deepens over Hudson Bay.


...Guidance Evaluation/Preferences...

Ensemble guidance continues to show a closed low cutting off from
the main flow in the Great Basin around Monday and then slowly
moving through the Southwest thereafter. There still remains a
large degree of east-west spread in the initial sharpening of the
trough and resultant location (then movement) as a closed low.
With a slight eastward shift in the guidance, followed the
consensus near the 00Z GFS/ECMWF and their ensemble means with
more emphasis on the ECMWF guidance by late in the period due to
its better consistency and preference downstream over the western
Atlantic (a bit slower with Jerry nearer to the NHC forecast).


...Weather Highlights/Threats...

Moisture from the remains of Imelda combined with a strong trough
in the northern stream will fuel a threat of locally heavy
rainfall from the mid-Mississippi Valley eastward through the
Midwest ahead of an approaching cold front. This may extend into
the Great Lakes/Northeast late Monday into early Tuesday but with
less areal coverage.

In the Southwest, tropical systems Lorena and Mario will lift
north-northwestward and their moisture will get drawn
north/northeastward ahead of the deepening troughing (eventual
closed low) out of the Great Basin early in the period. Southwest
flow aloft will intersect the approaching cold front and aide in
precipitation production initially over Arizona that may spread
into New Mexico as the upper low moves eastward.

Temperatures will generally be above average in the east/Southeast
and below average in the West. Overnight lows will be above
average for most areas CONUS-wide. Some record highs will be
possible from the central Gulf Coast through the Southeast Tue/Wed
with temperatures into the lower and mid-90s.


Fracasso


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

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:

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/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml