Area Forecast Discussion
Issued by NWS Portland, ME

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103 FXUS61 KGYX 150817 AFDGYX Area Forecast Discussion National Weather Service Gray ME 317 AM EST Thu Feb 15 2018 .SYNOPSIS... Expect another warm day today with temperatures reaching the 40s and low 50s. Weak low pressure moving through Quebec will slide a warm front through northern New England, bringing some clouds and a chance of light rain to northern areas. A cold front will move in from the northwest early on Friday, with low pressure tracking along this front Thursday night into Friday morning. This will bring some rain mainly to southern areas tonight. The front moves through early on Friday bringing a shift to a northwest wind and a return to colder weather. The coldest day will be Saturday as cold high pressure moves across the area. Low pressure south of New England may spread snow into the region Saturday night and early Sunday. && .NEAR TERM /TODAY/... Warm temperatures continue today. A shortwave trough in the northern stream sends weak low pressure east through Quebec today, with the associated warm front pushing northeast through New England. This reinforcing warm advection will allow temperatures to reach the upper 40s to low 50s today even though there will be a good deal of cloud cover. A southerly wind off the cold Gulf of Maine should keep temperatures a few degrees cooler across the eastern part of the area. There could be some light rain showers along the Canadian border as the warm front moves through. && .SHORT TERM /TONIGHT AND FRIDAY/... While the northern stream low moves into the Gulf of Saint Lawrence tonight it will send a cold front southeast toward New England. Meanwhile, a southern stream low will be tracking east across southern New England. This will spread some light rain into southern parts of the area overnight with temperatures holding in the 40s for the most part overnight. Good low level moisture over a melting snow pack will create the potential for fog, though confidence is not high enough at this point to mention dense fog wording. The cold front pushes across the area during the day on Friday. High temperatures will be around daybreak up north, while downsloping winds on the coastal plain will keep temperatures in the 40s in the morning before they begin a sharp fall in the afternoon as the stronger cold advection arrives. Locations along the Midcoast may actually see warmer temperatures Friday immediately behind the cold front than they see Thursday ahead of it! As the cold advection arrives, strong low level winds and good mixing should bring wind gusts to about 30 to 35 MPH for most of the area during the afternoon and evening. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... High Impact Weather Potential: * Potential for light snow accumulations Saturday Night through early Sunday. * Significant warm up becoming increasingly likely next week with potential hydro concerns. Pattern: Persistent pattern of the past few days continues early this morning with vortex centered just north of Hudson Bay...another over eastern Asia....with ridging just off the west coast of North America with early morning water vapor imagery revealing a shortwave helping re-establish troughing over the southwestern United States. Deterministic/ensemble guidance remains in strong agreement in maintaining this pattern through the coming weekend. Beyond this...there continues to be strong signals for a significant pattern change with Pacific ridge retrograding west and building...which allows significant troughing to take shape over western North America with a weakening/eastward shift of the Hudson Bay vortex. This favors building heights over eastern North America with a Bermuda high setup directing deep southwesterly flow along the eastern seaboard. The flow remains progressive through this period with no downstream blocking... so even this warm up does not look to remain with us for very long. Primary forecast concerns through the long term forecast period include potential weekend snowfall...then the focus turns to deep moisture plume along the eastern flank of developing longwave trough and how much precipitation potential we have from this feature. The Details... Friday Night - Saturday: High pressure builds in from the west Friday night...cresting overhead on Saturday...and then rapidly moves east. Airmass drying is very impressive...with PWATs falling below 0.1" overnight Friday night /-1 to -2 sigma/ with T8s closer to -1 sigma /-10C south to -15 to -20C north/. Gradient will rapidly weaken Friday night...which will allow for radiational cooling conditions to improve as the night goes on...and with dry airmass in place...expect that single digits are in reach away from the coast...with lower teens elsewhere. Seasonable day on Saturday as warm advection begins to develop with T9s -6C southwest to -10C northeast suggesting upper teens in the far north...with 20s to lower 30s to the south and east...just a bit colder than normal for this time of year. Saturday Night - Sunday: Models continue to struggle with this period as parent shortwave /now over Alaska/ dives south and east around the base of the Hudson Bay vortex and moves rapidly overhead while amplifying some as it does so. Ensemble sensitivity analysis shows that we/re still likely 12-24 hours before all parent features are well sampled by the RAOB network...and thus confidence is no higher than moderate through this period. The day to day changes in guidance confirms this uncertainty with the GFS now the most suppressed solution and the GGEM the most impactful. There is a gradually increasing consensus...however...around the idea of a glancing blow as low pressure moves south of the region after midnight Saturday night through Sunday morning...with light accumulations possible along the coast...with little snow inland. Still expect changes...and this will have impact on temperatures which will be warmer than on Saturday...but potentially capped given clouds/snow. Monday-Monday Night: High pressure will be centered just east of the region to begin Monday with warm advection and top down saturation rapidly setting in as the day progresses. Thus...expect an increase in clouds with rain showers approaching from the south and west towards evening. T9s moving to around the freezing mark should allow 40s for areas outside of the mountains. Showery precipitation looks to arrive Monday night and will likely take the form of rain for most location...with the potential for a mix at the onset over the mountains although even here temperatures aloft warm rapidly so the threat will more likely be from pockets of trapped low level cold air potentially leading to some freezing rain. Mild night with a non- diurnal trend likely /temps slowly rising through the night/ with 30s and potentially some 40s south. Tuesday - Wednesday: Substantial run to run and model to model differences develop by this time range with the EC/GFS/GGEM /and their ensemble counterparts/ all favoring a western trough... but very different evolutions along the eastern flank of this feature...reducing confidence. There is good confidence in temperatures moving well above normal for Tuesday and likely Wednesday with T8s at or above 10C. PWATs also increase dramatically as the Gulf of Mexico opens up. Looking at both the EC EPS and the GEFS...there is certainly enough overlap in guidance thinking to keep chance PoPs through this period...with the greatest precipitation potential favored west as current indications suggest that the best heavy rainfall signal will be west of our region. Certainly something to keep an eye on for potential hydro concerns. Otherwise...story will be temperatures...with good agreement that T9s move to near or above 10C Tuesday...with some potential to be warmer still on Wednesday. While this suggests the potential for 60s...have to be careful with precipitation potential as well as decreasing confidence... particularly on Wednesday. Still...boosting highs for both days with 40s north and 50s south is a good starting point that can be adjusted as confidence grows. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... Short Term...Mostly VFR conditions expected today, though there could be a brief period of MVFR ceilings as a warm front moves through today. Low pressure passes by to the south tonight and will bring some light rain to southern New Hampshire and coastal Maine along with MVFR to IFR conditions. Cold front moves through on Friday with northwest winds and clearing conditions outside the mountains. Winds during the afternoon could gust to 30KT. Long Term... VFR through Saturday evening. Potential for IFR/LIFR restrictions in snow late Saturday night through Sunday morning particularly for coastal terminals. VFR returns later Sunday through Monday. && .MARINE... Short Term...Southwest winds continue today, though remaining just below advisory levels. A cold front moves across the Gulf of Maine on Friday with increasing northwest winds in cold advection behind it. This could ramp up to gale force Friday evening. Long Term...Gale force winds over the outer waters diminish Friday night /have issued a gale watch this package for this likelihood/...with quiet conditions Saturday before low pressure south of New England brings the risk for renewed SCAs Saturday night and Sunday...particularly for the outer waters. Sunday afternoon/Sunday night again look quiet before increasing southerly winds again bring SCA potential for Monday. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Gale Watch from Friday afternoon through Saturday morning for ANZ150-152-154. && $$ NEAR TERM...Kimble SHORT TERM...Kimble LONG TERM...Arnott

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