Area Forecast Discussion
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000 FXUS61 KPBZ 191529 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1129 AM EDT Mon Mar 19 2018 .SYNOPSIS... Low pressure will bring a wintry precipitation mix to the Upper Ohio Region tonight, Tuesday, and Wednesday. Below normal temperatures set up shop the balance of the work week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Yet another sunny morning, which will be the last this week. Passing cirrus clouds this morning will give way to increase clouds from west, meanwhile stratus shall continue to expand along and east of the mountains and could reach Garrett and eastern Tucker counties this afternoon. There are indications of sprinkles across parts of Tucker county this afternoon from high resolution guidance, however given forecast low level moisture fields think any measurable QPF will hold off until after 0Z so removed pop mention for areas south of the mason dixon line late this afternoon. Otherwise, the remainder of the forecast is on track. && .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/... *** Heavy Wet Snow Possible in the Allegheny Front Tuesday night into Wednesday *** Confidence is increasing for potential for 8" or more of snowfall over 24 hours across the higher terrain of western Maryland and northern West Virginia, so a winter storm watch was issued. A weather-plethora, winter-spring battle is setting up to engage over the Upper Ohio Region for the short term period. Problems include model discrepancy and run-inconsistency as well as incidents of apparent feedback with overblown omega in the developing warm advection regime. Obs. and model world do agree that a southern stream low will dig over the Lower Ohio shunting relative warmth and moisture across WV and MD tonight, and finally over PA early on Tuesday. The warm surface (after another 50+ degree day) will be an inhibiting factor for travel issues for most areas in the event of light snow, or should warm advection be sufficiently strong for light freezing rain. The focus for problems thus remains on the ridges where dynamic cooling via falling pressure and southeasterly upslope is likely to support a temporal combination of freezing rain and snow development. As the aforementioned warm advection into the mid levels should inhibit dendritic growth potential, have limited potential snow amounts to advisory levels. In addition, the warm surface and eventual mid March sun angle should limit ice accumulation, especially after daybreak Tuesday; have thus lowered the ice from QPF ratio for the tonight/early Tuesday time frame. The bottom line is that advisory level winter precip is anticipated for the ridges, with much lesser confidence for other areas. A Hazardous Weather Outlook mention was thus included as per collaboration with neighboring NWS offices. For at least a portion of Tue, shortwave ridging in advance of the digging Lower Ohio storm system should diminish PoPs, while temperature rises into the 40s amid warm advection ahead of low pressure encroaching upon the Lower Ohio. Thereafter, the Lower Ohio low-center is progged to trundle slowly across the Mid Atlantic region through Wednesday, with coastal surface development enhancing boundary layer cold advection over the immediate area. Periods of light snow and snow showers are thus envisioned as the Upper Ohio is enshrouded on the northern flank of the mid level low, with inhibitions provided by daytime sun angle and a lack of mid level frontogenesis in a weakening wind field. && .LONG TERM /THURSDAY THROUGH SUNDAY/... Highlights: - No sign of Spring - Quiet to start - active end - Can`t say we have seen the last of snow Benign weather to commence this period with high pressure building south from the western Great Lakes. This will bring cool northerly winds into the region as daytime highs will remain in the 30s given H8 temps around -8C. Diurnal cumulus clouds will be abundant given cold air aloft. The surface anticyclone continues to drop slowly southeast overtop the Ohio headwaters Friday. Aloft there will be a passing shortwave trough, which will generate passing clouds, but given BUFR soundings illustrate dry low levels, do not foresee any measurable precipitation Friday. Mid level heights build this weekend, however at the expense of the warm advection, a warm front will cross the region Saturday afternoon / evening. Thermal profiles suggest there could be a wintry mix at the onset especially in the mountains and north of I-80 despite it beginning late afternoon / evening, which is a warmer part of the day. For now, will keep things a rain / snow mix with high pops. With the surface low track staying to our south on several models Saturday night into Sunday, far northern locations could stay all snow and see several inches of snow accumulation. At this time, locations south of I-70 should mix over to rain and stay rain for much of the event. Confidence is not high enough for a mention in the hazardous weather outlook per control run and ensemble spread, but as the week goes and we get through the mid week weather event, messaging can start for this /if needed/. With differences amongst long range guidance, this affects text bulletins and gridded temperature plots. MEX is about 5-8 degrees warmer than ECE guidance given track of weekend system. Will side with the cooler envelope that is not fully captured in the super blend guidance. && .AVIATION /16Z MONDAY THROUGH FRIDAY/... VFR conditions are expected through the TAF period as high pressure slides east. Clouds should increase today/tonight ahead of approaching low pressure, with precipitation beginning mainly south of Pittsburgh prior to 12Z. The form will be rain initially, but some freezing rain and snow may mix in overnight. OUTLOOK... Restriction potential returns with low pressure late Mon night thru Wed. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Winter Storm Watch from Tuesday afternoon through Wednesday afternoon for MDZ001. OH...None. PA...None. WV...Winter Storm Watch from Tuesday afternoon through Wednesday afternoon for WVZ512>514. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.