Quantitative Precipitation Forecast Discussion NWS Weather Prediction Center College Park MD 431 PM EDT Sat Mar 24 2018 Prelim Day 1, Day 2 and Day 3 QPF Discussion Valid Mar 25/0000 UTC thru Mar 28/0000 UTC Reference AWIPS Graphics under...Precip Accum - 24hr Day 1 ...Southeast/southern Appalachians into South/southern Plains... The vigorous, compact upper disturbance over the mid MS valley and western OH valley this afternoon will slide south and east toward the southern Appalachians, through the Southeast and off the Southeast coast over the next 24 hrs. However, a short wave diving through the nern quad of the country will sharpen the upper-level confluence and overall weaken the dynamic short wave. Thus still anticipate a healthy precip shield with decent rates to push through eastern KY/TN into swrn VA/western NC and nern GA before zipping through the Southeast. The guidance captures this scenario quite well and provided confidence in carrying 1-2 inch areal avg qpf amounts with locally higher values over the southern Appalachians, due to favorable orographics. Meanwhile, the associated surface cold front will eventually stall and become quasi-stationary across the South into the southern Plains Sun afternoon. This could trigger isolated showers/storms across the region, especially across northern TX into OK as lower upper heights from the west begin to reach the southern tier of the country. Overall WPC followed a model blend for QPF, which included global models and hi-res guidance. ...West into Upper Midwest... A couple of different upper-level systems will keep the West unsettled Sat evening through Sun. One upper-level short wave across the northern Rockies and inter-mountain West will lift north and east into central Canada and clip the northern Plains and parts of the Upper Midwest. Overall qpf amounts should be relatively light with this feature, though global models and hi-res guidance capture a streak of elevated moisture and an active low level jet for enhanced qpf amounts of likely rain mixed with snow across eastern ND. Meanwhile upstream, a closed mid to upper low over the eastern Pacific will move through northern CA and OR to reach the inter-mountain West/Great Basin. Marginal Pac moisture transport is expected with this system but expect the favored terrain and especially the northern CA coast into the northern Sierra with enhanced onshore flow and qpf amounts. Overall WPC stayed very close to the operational GFS and ECMWF on mass fields and qpf amounts. Day 2 Plains---Mid to lower MO Valley---Mid to Upper MS Valley The elongated upper trof centered from the northern Rockies into the Great Basin and into the Southwest at the end of the day 1 time period will be pushing steadily eastward day 2 and begin to separate into two distinct streams. The southern stream is expected to amplify into a closed low over the southwest Monday afternoon---while the northern stream height falls are more progressive pushing out of the northern Rockies into the northern high plains. Precipitation should begin to become more organized downstream of both branches of this elongated trof day 2 as pw values rise to 1 to 2 standard deviations above the mean through most of the Great Plains---lower MO Valley and Mid to Upper MS Valley in a region of fairly difluent upper flow with embedded shortwaves. Overall--it appears the precipitation areas should be fairly progressive day 2---limiting the heavy precipitation potential. Model consensus is for .25-.50"+ amounts across these areas. Accumulating snowfall potential will be confined to the northern portion of this broad precipitation area from the northern Rockies of north central WY---east northeastward into the northern high plains of northeast WY/far southeast MT---western SD and then farther to the northeast from eastern SD into central to northern MN. See the latest QPFHSD for additional winter weather information. Southeast into northern Florida A well defined frontal boundary will be dropping southward from the southeast into northern Florida day 2. PW values expected to pool to 1 to 1.5 standard deviations above the mean in the vicinity of this front---supporting widespread shower activity Sunday evening from southern GA into north FL. The low level flow is then expected to veer to a more easterly direction Monday along the east central to northeast FL coast with scattered showers possible in this onshore flow. Day 3 Southern Plains---lower MO Valley---Mid MS Valley into the OH Valley and Great Lakes The broad upper trof will remain split into two distinct streams day 3. There are timing differences with the slower moving southern stream with the GFS faster in lower heights into the Southern Plains while also being somewhat weaker with the southern stream closed low. This does have ramifications with the precipitation development day 3 from the Southern Plains---northeastward into the lower MO Valley and OH Valley. WPC is favoring the majority model solutions of being slower than the GFS with the height falls into the Southern Plains and subsequently slower to push the potentially heavy precip southeastward. Despite the mass field differences---there is consensus for developing widespread heavy precipitation this period across these areas which will remain in an axis of much above average pw values---2 to 3+ standard deviations above the mean---strengthening southerly to southwesterly low level flow into the frontal zone stretched southwest to northeast across these areas and in an overall favorable right entrance jet region. No significant changes planned to the day 3 excessive rainfall potential outlook with a a broad marginal and slight risk area stretching from north central TX into central to eastern OK---southeast KS---northwest AR---southern to central MO into southern IL. Areal average 1-2"+ precipitation amounts possible across these areas---with training of cells possible in a southwest to northeasterly direction parallel to the above mentioned front---supporting locally heavier to excessive amounts. The northern stream energy moving from the northern Plains into the Great Lakes will continue to be very progressive. This should keep precip totals on the moderate side .25-.50" through the Great Lakes day 3. Lee of the central to southern Rockies A separate precip max possible day 3 in the lee of the central to southern Rockies where the combination of post frontal upslope flow to the northwest of the southwest to northeast oriented front emanating from the southern Plains and large scale lift to the northeast of the southern stream closed low will support moderate to heavy snowfall totals across central to eastern CO into central to north central NM. Pacific Northwest Days 2 & 3 The westerly onshore flow off the northeast Pacific into the Pacific Northwest will be strengthening early Monday and remain strong through Tuesday. With pw values in this strengthening onshore flow expected to rise to 2+ standard deviations above the mean---moderate to heavy precip totals likely through the Washington/northern Oregon Cascades---west to the central to northern Oregon coast range into the Olympic range both day 2 and 3. Musher/Oravec Graphics available at www.wpc.ncep.noaa.gov/qpf/qpf2.shtml