textproduct: Gray - Portland

SYNOPSIS

On Tuesday a low pressure system will spread snow over the area and bring the first widespread accumulation to most areas south of the mountains. Moderate to heavy snow is likely to affect at least the afternoon and evening evening commutes on Tuesday before snow comes to an end. The storm track may still change and shift the heaviest snow amounts around, but most locations are expected to see some accumulations. Once that storm exits the region Wednesday, the rest of the week will be cool and breezy with mountain snow showers lingering.

NEAR TERM /TODAY THROUGH TONIGHT/

Key Message: Temperatures have dropped below freezing while surfaces remain wet from rain creating conditions favorable for black ice. Commuters this morning should be aware of slicks spots.

A secondary cold front crosses this morning bringing chances for snow showers in the mountains and gusty northwest winds. High pressure builds in from the west allowing skies to turn mostly sunny with highs ranging from the upper 20s north to upper 30s south.

High pressure crests over the area tonight allowing for cold conditions with lows in the single digits north to the teens across the south. These cold conditions will prime road surfaces for accumulating snow that will break out Tuesday morning.

SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/

Key Messages:

*A Winter Storm Watch remains in effect south of the mountains. Snow will break out SW to NE Tuesday morning with light accumulations impacting the morning commute.

*Snowfall rates will intensify through the afternoon approaching 1 inch per hour during the evening commute creating hazardous travel conditions with visibility dropping to one quarter a mile.

Forecast Details:

Latest available NWP guidance is in decent agreement that a deepening area of low pressure will track from New Jersey to southeast of Cape Cod Tuesday afternoon spreading snow into the region Tuesday morning. This low will progress ENE south of Nova Scotia Wednesday morning with snow tapering off NW to SE during the pre dawn hours. Available incoming 00Z guidance has started to converge on QPF while there remains a meaningful spread in ensembles. Notably the 00Z NAM has backed off the most with subtle downward trends in other mesoscale models. Current QPF forecast ranges from around 0.5 inches along southeast facing slopes to near 1 inch along the coast with around 0.3 inches north of the mountains.

In addition to ensemble spread in QPF, other points of uncertainty exist around the development of a quasi-stationary mesoscale snow band and the inland penetration of the coastal front. A mesoscale snowband acts to rob moisture from the northwest side of the band creating a tight gradient in snowfall while areas under the band could see up to a foot of snow. Latest hi res guidance also suggests the coastal front may push inland across SE New Hampshire and coastal Maine where snow may mix with or change to rain at times. The current snowfall forecast has not changed that much from previous forecast except for a slight decrease across SE NH and coastal York County and slight increase across interior central Maine. Given the impacts from this system are still over 36 hours away have opted to hold onto the Winter Storm Watch with this package. The going forecast calls for 6 to 10 inches across the Watch area with lower amounts along the immediate coast. Limited moisture will keep amounts north of the mountains in the 3 to 5 inch range.

Northeast to north winds will ramp up Tuesday evening through Tuesday night as low pressure treks east of the Gulf of Maine. Peak wind gusts will be around 25 mph along the coastal plain to 30 mph along the immediate coast. Snow tapers off after midnight from NW to SE with accumulating snow ending during the pre dawn hours. Lows Tuesday night will range from the teens north to the 20s along the coast.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Any leftover snow will wind down quickly early Wed morning...with northwest winds taking over and upslope snow showers developing. That will generally continue thru the remainder of the work week...with another stronger trof arriving over the weekend into early next week. The rest of the forecast beyond Tue night is NBM due to the focus on the storm.

One potential important thing to note is a strong arctic front is slated to move across the forecast area during the day on Thursday. It appears to be very sharp in the models and this may portend to a period of heavy squalls accompanying it. This bears watch. In the immediate wake of the front later Thursday winds could get close to advisory criteria. Wind chills are likely to be the coldest of the season thus far Thursday night.

AVIATION /04Z MONDAY THROUGH FRIDAY/

Short Term...Conditions improve into sunrise with VFR likely today through tonight. NW winds will gust 20-25 kts around mid day. Clouds thicken and lower late tonight with snow overspreading the area Tuesday morning. IFR to LIFR conditions are likely late Tuesday morning into Tuesday night in snow that could reduce visibility to 1/4 mile at times. Conditions improve to VFR from NW to SE late Tuesday night.

Long Term...Storm pulls away and winds turn northwesterly VFR returns quickly to places south of the mtns Wed AM...while HIE will likely see a continuation of upslope clouds and snow showers with local MVFR. A sharp cold front is expected to move across the forecast area from W to E Thursday. This could mean snow squalls and very gusty SFC winds.

MARINE

Short Term...A secondary cold front crosses this morning bringing NW winds gusting to 30 kts near the bays and Gale force along the outer waters this morning. High pressure crests over the waters tonight allowing winds to subside. Low pressure tracks near the Gulf of Maine Tuesday afternoon bringing building seas and possibly Gales in its wake Tuesday night.

Long Term...Winds are expected to diminish markedly as the day progresses on Wednesday. However they are likely to increase once again to SCA levels Wed night ahead of the next cold front. Gales likely Thu into Fri in the wake of arctic front.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Storm Watch from Tuesday morning through late Tuesday night for MEZ012>014-018>028-033. NH...Winter Storm Watch from Tuesday morning through late Tuesday night for NHZ004>015. MARINE...Gale Warning until 10 AM EST Monday for ANZ150-152. Small Craft Advisory until 10 AM EST Monday for ANZ151. Small Craft Advisory until 7 PM EST Monday for ANZ153-154.