Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 423 PM EDT Sun Mar 25 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Mar 26/0000 UTC thru Mar 29/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Pacific Northwest... A rather impressive short wave trough moving rapidly across the nern Pacific towards British Columbia will yield zonal moist onshore flow into WA and extending south into OR over the next 24 hrs. This upper disturbance and lower heights will not dig much at all, due to the mammoth upper ridge over the eastern Pacific and extending into the northwest quad of the country. However, an anomalous long fetch of Pacific moisture flux will begin reaching the coast overnight and persist through Monday. Overall WPC followed a blend of the GFS/ECMWF with the 12z hi-res package for areal avg totals of 1 to 2 inches with locally higher values in the coastal ranges, Olympics and Cascades. ...Central Rockies into Plains/Mississippi Valley... An amplified split flow upper trough will move slowly through the West over the next day, while the leading edge of upper height falls and upper disturbance along the subtropical jet emerge into the central portion of the country. This will be the start of a multi-day active convection and heavy to excessive rainfall event, truly a spring pattern. While moisture and precip will increase throughout the period from large scale warm advection and ideal broad swrly upper difluence, a couple of spots may see more enhanced qpf amounts. The first area is across WY into western SD, as a mid to upper low and well-defined 500mb vort tracks across the state into the front range of the northern to central Rockies. The guidance captures a wave of surface low pressure or inverted surface trough sliding through WY to enhance the vertical lift and upslope/orographic flow. Expect areal avg amounts up to an inch, locally higher, from the Wind River range to the Big Horn mtns to the nern portion of the state to western SD. Meanwhile, out over the Plains and/or invof a warm front lifting north and dry line remaining relative stationary, expect an increase in moisture pooling and instability leading to convective heavy rains from sern NE/swrn IA through eastern KS/western and central MO and slicing through nern OK to north central TX. Overall WPC used a blend of the GFS/ECMWF/HREF Mean and NBM with the NAM Nest and ARW for coverage and amounts across the entire region. ...Eastern Gulf Coast States... A quasi-stationary frontal boundary from nern FL back into southern AL/MS may yield locally heavy rain with overall a light steering mechanism. The hi-res shows a signal for locally heavy amounts and WPC increased qpf amounts over the global models from JAX to MEI/JAN. Days 2 & 3 Southern Plains---Lower MO Valley-Lower to Mid MS Valley---Lower OH Valley---Lower TN Valley There is a strong model signal for the upcoming day 2 & 3 time period for widespread heavy rains across portions of the Southern Plains---northeastward into the Lower to Mid MS Valley...Lower TN Valley---Lower MO Valley into the Lower OH Valley ahead of the well defined and slow moving closed low pushing from the Southwest into the southern high Plains days 2 & 3. With PW values expected to rise to 2 to 3 standard deviations above the mean and very favorable right entrance region jet dynamics pushing slowly eastward across these areas---confidence is high for the widespread heavy totals. The axis of much above average pw values will be slowly sinking southeastward during the day 2-3 time period---with potential of training of precipitation areas in this axis in a southwest to northeasterly direction parallel to the deep layered mean flow. Recent dry conditions over the past few weeks over the Southern Plains into the Lower to Mid MS Valley---Lower TN Valley are keeping stream flow...as per the national water model---low and subsequently high ffg values. Still---with potential for training of precip areas in a southwest to northeasterly direction---runoff issues will be possible. At the moment---there were only some slight changes made to the day 2 excessive rainfall potential---12Z Mar 26- 12Z Mar 27th---extending the slight risk farther southwest into south central OK and far north central TX. For the day 3 excessive rainfall time period...12Z Mar 27th to 12Z Mar 28th the slight risk was extended slight to the southeast into northeast TX and far northwest LA---but otherwise maintained a broad slight risk area from northeast TX---far southeast OK---most of AR into southeast MO---southern IL and far western TN and far western KY. Areal average 1 to 3 inch totals likely both days 2 and 3 across these areas---with isolated heavier totals in areas of training. Upper MS Valley---Great Lakes---northern Mid Atlantic into the Northeast Height falls moving east northeastward in the northern stream flow from the Northern Plains---Upper MS Valley--upper Great Lakes and into southeast Canada will be much faster moving than the above mentioned slow moving southern stream closed low. This will result in faster moving areas of precip day 2 from the Upper MS Valley through the Great Lakes and across the northern Mid Atlantic into the Northeast day 3. This will limit heavy precip potential across these areas with moderate totals in the .25-50"+ range expected. Central to Southern Rockies into the lee of the Central to Southern Rockies day 2 Accumulating snows likely day 2 across portions of the Central to Southern Rockies into the lee of the Central to Southern Rockies in a separate precipitation area to the northeast of the slow moving southern stream closed low moving east through the Southwest. Post frontal upslope flow combined with large scale lift to the northeast of this closed low will support moderate to heavy snows over central to eastern CO and north Central NM. See the latest QPFHSD for additional winter weather details. Pacific Northwest into the Northern Rockies The strong westerly onshore flow that begins into the Pacific Northwest during day 1 will continue through all of the day 2 time period and then weaken during day 3. Additional moderate to heavy precip totals likely day 2 from the northern Rockies of northern ID/northwest MT and across the Cascades and coast range/Olympic Range of Washington state. Mostly moderate precip totals expected day 3 across these areas and expanding southeastward into the northern high plains and Rockies of WY. Musher/Oravec Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml