Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 359 AM EST Sun Mar 04 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Mar 04/1200 UTC thru Mar 07/1200 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Northern Rockies/Northern Plains... A mid- to upper-level low moves from Oregon into the northern Plains, aiding the spin-up of a Colorado low which then progresses northeast into South Dakota. There has been a trend towards increasing surface troughing/850 hPa frontogenesis across Montana which had led to some increase and westward expansion of QPF within the model guidance. After coordination with the Great Falls, MT forecast office, trended westward in suit. Across the northern Plains, the pattern is messy with a pair of areas with good low- to mid-level frontogenesis which shift east with time. Overall, resemble a compromise of the 00z GFS, 12z ECMWF, and the 00z mesoscale guidance which kept reasonable continuity. Much of this precipitation is expected to be in the form of snow -- see our Winter Weather suite of products for more information on winter weather impacts. ...Lower to Mid-Mississippi Valley... A return flow of moisture near the surface from the Gulf of Mexico, with a continued connection aloft from offshore Baja California, is expected to interact with a warm front to generate showers and thunderstorms from the ArkLaTex into Missouri and southeast Iowa. The southern limit of any hydrologically significant precipitation is expected to be marked by the 6C isotherm at 700 hPa across Texas and Louisiana. Precipitation is expected to be progressive this period before a new batch reloads near the ArkLaTex on day 2/Monday. After looking at GFS mass fields, went with a precipitation pattern slightly wetter than the 00z ECMWF which was an increase from the previous WPC QPF. Days 2/3... ...Northern and Central Rockies across the northern Great Plains eastward... An upper trough that had started over the northern and central Rockies will just about be clear of the Rockies front range as the day 2 forecast begins on Monday morning and the development of a surface low should be well underway. The system will then go through an occlusion process which slows the forward motion from Monday into Tuesday. It becomes more progressive late on Tuesday as it begins to interact with a mid level system moving southward from James Bay. This helps to ease the mid level center across Iowa and into far northwest IL by the end of day 3. Precipitable water values around 0.75 inch will be advected into the northern plains on a 45-55kt southerly jet ahead of the low by Monday. Warm rainfall...occasionally falling with moderate rates...falling on the snowpack may cause areal flooding concerns...but not flash flooding as of this time. A deformation zone sets up on the north side of the low from WI into lower MI Monday night...but with occlusion comes weakening and decreasing precip rates for Day 3 across this area. Precip type is of concern with this system...please refer to WPC's Heavy Snow Discussion (QPFHSD) for more details on winter weather...especially from the Dakotas into parts of Minnesota. ...Central Plains to Midwest... Moderate rainfall is likely from the central plains across the Midwest with the frontal system pushing ahead from the slow-moving, occluding system initally over South Dakota. Amounts should be kept in check given the progressive nature of the front and the fact that the airmass ahead of the front will typically be under an inch. Given the steady, eastward progression, we refrained from oulooking the area for a risk of excessive rainfall. ...Gulf Coast and Deep South... The cold front ahead of this low drapes from east TX and pivots to a more east-west orientation through Monday night as it spreads to GA/SC. PW of 1.50 inches is two standard deviations above normal which may allow a narrow swath of areally averaged one to two inches of rainfall near the gulf coast. The 00Z model runs still showed some spread on day 3...with some of the usual model biases becoming evident. The ECMWF remained slow and had a longer duration of rainfall along the Gulf coast before pushing the area of rain southward along the Florida peninsula and adjacent waters. The GFS was much faster with its southward push...and the NAM sided with the GFS on a faster solution but it was not as fast. Based on the latest guidance, still think that an excessive rainfall outlook area is not warranted at this time given the placement of the heaviest rainfall and the expected forward speed of the front and associated rainfall. However any inland shift would raise the specter of flooding. Roth/Bann Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml