textproduct: Gray - Portland

SYNOPSIS

High pressure will slowly give way to developing southwest flow which will draw in warmer air and bring many in the region their first above normal temperature day since Thanksgiving. A weak and mostly dry front will cross the area around Wednesday, and then southerly winds really begin to increase Thursday and Friday. Temperatures by Friday may climb into the 50s and rainfall is likely even into the mountains. It does not look to be heavy enough or long enough to wipe out all of the snow, but it does look like it will be windy Friday, especially near the coast. Southerly gusts of 40 to 50 mph are possible. After that the pattern looks like it will remain active. We get the briefest of breaks on Saturday before the next chance of precipitation arrives Sunday.

NEAR TERM /UNTIL 6 PM THIS EVENING/

640am Update...Overcast has been resilient across southern and central NH early this morning, with much of this moisture drying in the lee of mtns for western ME. Will likely see these overcast skies continue for a few more hours before the better moisture lifts north. Can't rule out a flake or two in western and northern NH as light radar returns track in from NY/VT.

Previous Discussion... Another cool day is expected today as the H5 pattern begins to flatten with sfc ridging remaining across New England. It will be a little warmer than Monday though as T8s warm to around +12C, which will allow high temperatures to reach the 20s to lower 30s from north to south. It will also be less windy as winds become southwesterly, so it won't feel as cold.

SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/

Partly cloudy skies will prevail tonight with southwesterly flow at the surface. Low temperatures will primarily be into the teens.

Clouds will increase during the day on Wednesday as a frontal boundary and accompanied s/wv trof begins to approach western New England. It will remain mainly dry though except for a few scattered snow showers across the mountains and towards the Canadian Border. High temperatures will be noticeably warmer with readings into the 30s to lower 40s from north to south. Wednesday night will remain dry behind a weak cold front with lows into the teens and 20s.

Clouds will increase during the day on Thursday ahead of our next storm system. It should be a dry day though once again with high temperatures into the lower to middle 40s.

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/

Key Message: Above normal temps with rain expected Fri but trending back towards normal by next week. Winds are looking increasingly gusty on Fri ahead of the approaching system.

Impacts: While rainfall amounts and temps are not expected to cause significant snowmelt enough for flooding concerns...southerly wind gusts are starting to looking more robust. The forecast continues to ramp up...and wind gusts in the 40 to 50 mph range are not out of the question Fri.

Forecast Details: A sharp..negatively tilted trof will swing across the Northeast Fri. As a result the forecast is trending towards a faster moving but potentially hard hitting frontal passage.

The hard hitting may come in the form of strong southerly winds during the day ahead of the front. Ensemble guidance continues to ramp the low level jet with time. NAEFS return period guidance suggests the latest run has a roughly once every 10 year southerly 850 mb jet. Additionally the ECMWF EFI sits at 80 to 90 percent at this time...meaning that most of the ensemble members show a significant wind gust event for much of the forecast area south of the mtns. The trend of that forecast is also notable...as it has showed a steady run to run increase in members showing significant wind gusts. Based on local research the forecast low level jet strength would lead to fairly widespread 35 kt gusts along the coast. At this time the NBM forecast is lower than 30 kt for most of the area...so I am leaning towards bumping those up a good 5 to 10 kt across the board. I would not be surprised if subsequent forecast updates have to increase winds further.

As precip moves into the region early Fri it is possible that wet- bulb cooling may tend towards an in-situ cold air dam...but there is little preventing the warm air from invading. By midday Fri 925 mb temps approaching +10C are forecast to push towards the St. Lawrence River. Given that forecast I do not see much snow even for the higher elevations.

The mean QPF is also generally below 1 inch for the event given how quickly it moves thru the region. DESI cluster analysis indicates that amplifying the pattern...i.e. deeper trof and stronger downstream ridging...would lead to more widespread QPF at or above 1 inch. At this time that looks like about 1 in 5 members...so a low but not totally unlikely chance. Overall given the forecast I think the snowpack should be able to absorb much of the rain...especially where locations have more than 3 inches on the ground.

Otherwise the extended looks like it returns towards near to below normal temps after this system but the pattern will remain active. No significant changes were made from the NBM beyond Fri.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Short Term...VFR conditions will prevail through the period. The possible exception is at KHIE where intermittent periods of MVFR CIGs are possible at times due to lower ceilings and -SN. Overcast skies hang on for a few hours this morning, generally thinning into the afternoon. Winds will be primarily out of the W-SW at 10-15 kts. Approaching LLJ this evening and overnight may bring LLWS to at least northern NH and western ME terminals.

Long Term...Widespread IFR or lower conditions will develop Fri as warm air surges over the cold interior snowpack. It is even possible that some daytime fog develops. One exception to the IFR conditions may be just north of the White Mtns where downsloping winds help to scatter out the low clouds...this includes HIE. Also near the coast is looking increasingly gusty. Conservatively I am thinking southerly surface gusts of 30 to 35 kt. At this time winds look largely unidirectional though...so more of a turbulence vs LLWS scenario. Once the cold front sweeps thru precip will taper off and conditions should return rather quickly to VFR...with MVFR CIGs lingering the mtns. Narrow high pressure maintains VFR Sat...but another chance for precip arrives Sun. This looks cold enough for snow...so areas of IFR are possible if this stays far enough south to move thru the forecast area.

MARINE

Short Term...SW gales are possible late Tuesday night through Wednesday evening with gusts up to 40 kts for all waters except Casco Bay where gusts to 30 kts are possible. Seas will build to 6-10 ft outside of the bays. Winds and seas will then briefly diminish during the day on Thursday before increasing again towards Thursday evening.

Long Term...Southerly winds continue to steadily increase thru Fri. Strong gales are looking more likely for all waters...especially outside the bays. There is a chance for storm force gusts as well if forecast trends continue. Winds will shift to westerly late Fri but remain gusty...and a period of westerly gales is possible into early Sat. After a brief period of conditions below SCA thresholds...SCAs may develop again behind a warm front Sun.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Gale Watch from late tonight through Wednesday evening for ANZ150>152-154.