textproduct: Gray - Portland

SYNOPSIS

The first widespread winter storm is expected to bring a plowable snow to much of the region the remainder of today and into tonight. The weather will briefly turn quieter on Wednesday before an Arctic cold front brings snow squalls and breezy conditions Thursday afternoon and evening before temperatures turn sharply colder to end the week. Additional snow shower activity is possible again this weekend as a series of disturbances cross the region.

NEAR TERM /UNTIL 8 AM WEDNESDAY MORNING/

850 PM Update...Going forecast is in good shape and have mainly tweaked PoPs and pulled in observed temperatures. Low pressure continues to deepen as it is now making its closest pass to the area as it skirts SE of Cape Cod. Latest radar shows a couple of narrow snow bands starting to consolidate from Carrol County through southern Somerset County and another axis of heavier precipitation pushing into coastal SW Maine. There has been some sleet mixing at the immediate coast. Latest guidance suggest that snowfall rates under the band across the interior will be around 0.5 to 1 inch per hour as it slowly pivots south and east. Snow will likely continue for several more hours south of the mountains across western Maine into eastern NH with additional amounts around 2-4 inches.

Previously...

Generally light to moderate snow continues across the area with occasional bursts of heavy snowfall. This has been due mainly to broad warm advection lift in the right entrance region of a strong upper level jet streak. There has also been a more concentrated mesoscale band from convergence around H7...and under this snow totals are approaching 6 inches already.

From this point forward into the evening the upper level divergence will begin to better collocate with mid level convergence as those levels continue to deepen and close off. When that occurs precip rates will tend to remain moderate to heavy. What I am watching closely is temps along the coast tracking the location of the coastal front. Temps are dropping along the Midcoast as the front drifts east. Hi-res model guidance generally indicates that the coastal front is forecast to push west only for the next two hours or so...maybe a little longer for Penobscot Bay...before deepening low pressure passing our longitude drags it east again. So my gut feeling is that if it has not significantly warmed up along the coast by now it is unlikely to do so from this point forward given how far offshore the front is for areas southwest of Muscongus Bay. Snowfall rates thru evening will be 1 inch or more per hour at times...especially under the largely stationary band paralleling the storm track. As a result snowfall amounts are higher than previous forecasts especially for coastal southwestern Maine into Rockingham County NH. However there have been no changes in headlines as these areas were already in a winter storm warning.

Late tonight low pressure will continue to pull east and winds turn northwesterly and begin to downslope. This will end snowfall quickly...but not before even those areas around Penobscot Bay which will have been mostly rain flip to a period of snow.

SHORT TERM /8 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/

Low pressure continues to quickly depart to the northeast on Wednesday, allowing shortwave ridging to build in. This bring a day of benign weather with temperatures generally in the 30s with partly cloudy skies and decreasing winds.

Clouds increase Wednesday night which will keep the cooling potential in check with the fresh snow on the ground. Temperatures will probably level off in the 20s for most, but temperatures in the 10s are possible if there are periods of less cloud cover

LONG

A shortwave trough will push a potent arctic front through New England on Thursday with snow showers accompanying this front. Steep low-level lapse rates, sufficient moisture, a small amount of CAPE and favorable winds aloft suggest that heavy snow showers and/or snow squalls are possible with this front from late morning into the early evening hours (supported by snow squall parameters of 2 to 4 from the NAM and GFS). This also applies downwind of the mountains and even all the way to the coast as Froude numbers will be well above the supercritical level of 2.

Winds become breezy Thursday evening and night behind the front with a very cold airmass moving into the region. The combination of the winds and temperatures will likely push wind chills below zero for most of the area overnight into the early part of Friday morning. Fortunately the winds diminish through the day Friday, but it will be a cold day with highs remaining in the 20s and even 10s in the mountains. If clouds can hold off, Friday night will be favorable for efficient radiational cooling with lows in the single digits possible if skies do remain clear enough.

For the weekend, a weak disturbance could bring snow showers to parts of the area on Saturday with the mountains possibly seeing lingering upslope precip into Sunday, but probabilities for over an inch of snow are low (10-30% from the ECMWF and even lower from the GFS).

High pressure builds into Sunday into early next week with mostly dry conditions through at least Monday and temperatures remaining colder than normal.

AVIATION /02Z WEDNESDAY THROUGH SUNDAY/

Short Term...Mostly LIFR conditions across the area at this time and snow continues for most areas. Coastal front remains onshore for parts of the Midcoast...leaving RKD MVFR with light rain. Even there by this evening I expected winds to shift to more northerly or northwesterly and precip will change to snow. So IFR or lower conditions continue until between 04z and 08z for TAF sites...generally ending west to east.

Long Term...VFR expected Wednesday and Wednesday night. A strong cold front moves through Thursday, bringing a chance of scattered but potentially heavy snow showers and/or squalls. These could bring brief instances of IFR or lower restrictions should they pass over any terminals. Mainly VFR Thursday night and Friday behind the frontal passage, but wind gusts to 25-30kt are possible late Thurs and into early Friday behind the fronts with winds then easing through the day Friday. A weak disturbance could bring some light snow and flight restrictions on Saturday into Saturday night with perhaps some upslope snow showers lasting into a part of Sunday for HIE.

MARINE

Short Term...No changes to the coastal waters forecast thru tonight. The coastal front remains offshore for most of the waters south of about Boothbay Harbor. It continues to drift slowly east along this southern end...setting up east of Isles of Shoals. To the east of that boundary it will remain rain...while west will be be snow or a snow/rain mix bringing lower visibility. Tonight as the coastal storm pulls away winds will shift to northwesterly and become gusty for a time. Gale warnings remain in effect outside of the bays...with SCAs expected inside.

Long Term...Winds and seas relax Wednesday into Wednesday night as the low pressure departs high pressure gradually builds in. Winds should fall below SCA levels by the afternoon, but seas will likely remain at or above SCA thresholds. For Thursday, a potent arctic front approaches and crosses through, likely bringing another period of gales to both the bays and outer waters into Thursday night. There may even be some gusts to Storm Force over the outer waters. High pressure then builds in and shifts to the southeast on Friday with possible SCA conditions for at least the first part of Friday. Conditions improve going into the weekend, but a weak disturbance may bring a brief period of SCA conditions. High pressure builds in from the west Sunday into Monday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory until 4 AM EST Wednesday for MEZ007>009. Winter Storm Warning until 4 AM EST Wednesday for MEZ012>014- 018>028-033. NH...Winter Weather Advisory until 4 AM EST Wednesday for NHZ001>003. Winter Storm Warning until 4 AM EST Wednesday for NHZ004>015. MARINE...Gale Warning until 10 AM EST Wednesday for ANZ150-152-154. Small Craft Advisory until 10 AM EST Wednesday for ANZ151-153.