textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes with this forecast update.

KEY MESSAGES

1. A late week coastal storm remains possible with rain and/or snow. Confidence is low, but winter conditions remain possible for at least parts of the forecast area.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Shortwave trof has crossed the forecast area earlier this evening. Showers petered out south of the mtns, but cool/moist upslope flow will continue thru sunrise. Clouds and showers will remain upstream of the ridgelines perhaps until this evening. That is when heights begin rising slightly and mid level flow starts to turn more southwesterly and less upslope.

A positively tilted H5 trof will move across the Great Lakes on Wednesday night into Thursday as a sfc low develops near the OH Valley and then swings offshore of the Mid-Atlantic coast Thursday night. This low is then progged to move northeastward towards Cape Cod into Friday before exiting near Newfoundland by late Saturday. A fairly large spread in guidance continues this evening in terms of the eventual track of this low and the severity of any possible impacts across the local region.

Latest 18Z guidance has trended upward a bit on QPF, with latest probabilities for >=0.50" now generally between 50-70%, highest south of the mtns. This is due to a slightly more westward track along with a longer residence time of precipitation, which could begin as early as Thursday afternoon and then persist in waves through part of Saturday. It is too early to determine if this trend will persist as we get closer in time or if guidance will trend drier once again. In terms of precipitation type, while snow accumulations are less likely south of the foothills, some festive flakes cannot be completely ruled out all the way to the coast along with southern portions of the forecast area. The highest potential for some wintry driving conditions continues to be favored from the foothills and points north, especially during the nighttime and early morning hours when solar insolation is not a factor. We will continue to monitor this system over the coming days as forecast details become clearer.

Once the coastal storm pulls away, high pressure builds down into the CONUS from the Canadian Prairies. There will be some moderation of temps over the Great Lakes, but overall it looks a favorable set up for temps to average below normal. Daytime highs should be near normal, but ideal radiational cooling early next week should allow overnight readings to fall well below normal.

AVIATION /02Z WEDNESDAY THROUGH SUNDAY/

Through 06Z Thursday: VFR conditions expected at all terminals thru morning. The exception will be HIE, where upslope winds will keep MVFR hanging around thru sunrise. An occasional shower cannot be ruled out either, but not high enough confidence to include in the TAF at HIE. CIGs will lift at HIE during the day and all terminals are expected to be VFR with westerly breezes. Increasing clouds and lowering CIGs are expected to develop west to east tonight, but may remain VFR at all terminals until Thu.

Outlook:

Thursday/Thursday Night: Deteriorating flight conditions are likely as RA arrives from W-E and ceilings lower. Generally NE winds of 5-15 kts. Moderate forecast confidence.

Friday/Friday Night: Lingering restrictions due to RA and low ceilings. Some SN may mix in at times, especially across inland TAF sites. Gusty NE winds possible, especially along the coast with gusts approaching 30 kts. Moderate forecast confidence.

Saturday/Saturday Night: Lingering restrictions possible due to RA/SN and low ceilings. N winds of 10-20 kts. Low forecast confidence. Sunday/Sunday Night: Improving flight conditions with NNW winds. Moderate forecast confidence.

MARINE

Gusty northwesterly winds continue thru mid morning in the wake of a cold front crossing the waters. SCA remains in effect for the coastal waters. There is moderate confidence for an area of low pressure to move offshore of the Mid- Atlantic coast Thu into Fri before moving northeastward through this weekend. While there remains considerable uncertainty in the track of this coastal low, increased northeasterly winds and building seas are likely. Gale force wind gusts may be possible on the coastal and outer waters.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 10 AM EST Wednesday for ANZ150-152- 154.