textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes since the last forecast package. An active pattern remains likely through the weekend, with multiple chances for light to moderate precipitation events.

KEY MESSAGES

1. Light snow has developed to the northwest of New England and will overspread the area through the morning. Snow accumulations will generally be less than an inch, but could cause surfaces to become slick during the morning commute.

2. A narrow axis of snowfall will develop west to east across New England Wednesday through Wednesday night. Light to moderate snowfall accumulations will bring potential for slick travel Wednesday afternoon into Wednesday night across southern NH and far southwest Maine. Some north or south shifts in the axis of snowfall remain possible.

3. Active pattern continues Friday into early next week with one to two areas of low pressure developing near southern New England.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Warm air advection associated with low pressure passing through Quebec has led to an area of light snow to develop to the northwest of New England. A look at latest radar vs observations suggest that low level dry air is limiting snow from reaching the surface. Model soundings suggest modest increases in low level moisture over the next 6 to 12 hours will allow for intermittent light snow to overspread the area with accumulations generally less than an inch. Nevertheless a coating of snow is possible through the morning commute that could produce slick surfaces.

Temperatures will rise above freezing south of the mountains with any snow showers changing to rain showers. Dry air aloft and temperatures near freezing in the mountains could result in brief wintry mix or freezing drizzle this afternoon. A cold front crosses tonight allowing for any wintry mix in the mountains to change back to snow showers.

KEY MESSAGE 2 DESCRIPTION...

A frontal zone will sharpen across New England Wednesday into Wednesday night as mild southwest flow over the Ohio Valley collides with cold and dry northerly flow originating from SE Canada. This dry northerly flow will produce a sharp gradient in the northern extent of accumulating snowfall that develops along the frontal zone. Latest available 00Z guidance generally keeps accumulating snow along and south of a line from KLEB to KPWM with some solutions keeping snow as far south as the NH/MA border. However there remains some more bullish ensemble members and the RRFS that bring accumulating snow as far north as the White Mountains towards the Capital district of Maine. Have mainly stuck with the NBM as it has consolidated likely PoPs across southern NH while maintaining slight chances as far north as the White Mountains into central Maine. The going snowfall forecast calls for 1-3 inches from KLEB to KPWM and points southward with locally higher amounts in the Monadnock Region. The timing of this snowfall will likely bring the potential for slick travel during the Wednesday evening commute. Any northward shifts in the axis of snowfall would result in higher accumulations from south to north.

KEY MESSAGE 3 DESCRIPTION...

Two systems appear to approach the northeast over this weekend. The first is a mature low that should occlude over the Great Lakes on Friday, allowing for a burst of snowfall Friday night through some mixing can not be ruled out in southern NH. Snowfall probabilities indicate around a few inches of snow is likely. Snow could make roads slick Friday night and Saturday morning.

By the start of next week, we are keeping a close eye on a coastal low that may impact the northeast. Models currently keep the system just to the east of the Gulf of Maine, with only light snow in the forecast for now. However, if the storm track deviates any further north or west than where it is currently, the storm could bring measurable snowfall to the region.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

Through 00z Wednesday...Patchy MVFR deck will continue to invade along coastal terminals and into southern NH TAF sites. Some uncertainty how thick this layer continues overnight, but should see continued lowering into the morning hours Tuesday. Light SN will accompany this invasion from the west, reducing vis to MVFR/IFR between 12 and 18z. Cigs may scatter Tuesday afternoon while cloud bases will be around MVFR/IFR thresholds.

Outlook...

Tuesday Night and Wednesday: Clouds with be SCT/BKN Tuesday night while cigs will remain around MVFR/IFR thresholds. Highest confidence in continued MVFR to IFR with be at KHIE. Clouds thicken and lower from south to north Wednesday with chances for snow along and south of line from KLEB to KPWM.

Wednesday Night: IFR likely at KMHT, KCON, and KPSM through first half of Wednesday night in snow. VFR north of KLEB to KPWM with improvement north to south into Thursday morning

Thursday and Thursday night: VFR. No sig wx.

Friday and Saturday: Another system brings chances for snow and flight restrictions.

MARINE

Winds remain below 25 kts through Wednesday with SW winds today shifting NW Wednesday as a weak system passes north of the waters. Wave heights will approach 5 feet Tuesday night through Wednesday night along the outer waters. Northerly winds freshen Wednesday night with gusts approaching 25 kts. Winds and seas drop below SCA thresholds Thursday.

Low pressure developing near southern New England Friday into Saturday will bring potential for at least SCAs.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...None.