textproduct: Gray - Portland

WHAT HAS CHANGED

Minor update to the Aviation section for the 12Z TAFs.

KEY MESSAGES

1. After some early morning fog today, the day should be mostly dry and cloudy. There is a chance of late day showers across southern NH. Friday will likely be dry.

2. Rain chances both weekend days with a frontal system nearby.

3. Drier conditions to start next week, but clouds/showers remain possible in the interior.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Fog will lift by mid-morning today, and another seasonable day is expected temperature-wise with highs in the mid 70s to lower 80s along with a good deal of clouds. Most of the forecast area will likely remain dry today but there are still some guidance members showing the northern fringes of a system moving to our south to clip our southern zones later in the day. Therefore, we will retain a chance of showers for southern zones, mainly for southern NH into the evening hours.

High pressure settles in for Friday with fair and dry weather and lower dewpoint values. Will disregard the outlier HRRR at this time which bring showers to southern zones during the afternoon and evening.

KEY MESSAGE 2 DESCRIPTION...

An initially stalled front well south of New England will start its climb north towards the region as a warm front on Saturday. One or more waves of low pressure will ride along this boundary, bringing an unsettled weekend with periodic rain chances. One complexity to this setup is two separate waves of moisture; one originating from the Southeast U.S. on low-level southerly flow, while from the west will be a 500 mb trough amplifying, and likely resulting in a surface low developing. It is unclear exactly how these two features interact, with a range of outcomes from a full phase with locally heavy rainfall, to two separate rainfall maximums, which may or may not be over the forecast area. What is known however is it will be a rather moist environment with dew points surging to the upper 60s and ensemble PWATs on the order of 1.5-1.8", which is a respectable signal for this range. NBM mean for precip is generally only around half an inch however, likely owing to uncertainty over the extent/spatial coverage of precipitation both days this weekend. So, hope is not yet lost for some dry hours (although rainfall is badly needed).

CIPS/CSU machine learning guidance indicates a low risk for strong- severe storms on Sunday, which is the best chance we have to get into the "warm sector" with guidance indicating highs possibly reaching the low 80s in spots. Right now shear looks quite poor however, so not overly intrigued with things as they stand currently.

KEY MESSAGE 3 DESCRIPTION...

The upper-level low to our west takes over as the main driver of local weather to start next week, with current indications that it may fully close off and stall over Quebec. This would bring cyclonic westerly flow to New England to start the week, with some mixed signals whether it is more of a dry or moist wrap-around flow. Based on QPF signals and local pattern recognition, there will likely be some upslope-driven clouds and vertically-shallow precipitation in the White Mountains and surrounding higher-terrain in the interior, with conditions most likely to be dry closer to the coast. Despite slightly cool temperature anomalies aloft, highs likely stay near average with some downslope warming effects towards the coastal plain.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Through tonight...Marine fog/stratus at RKD and valley fog at LEB should dissipate by 13-14Z. Otherwise VFR is expected today. Some -SHRA will be possible across southern NH late this afternoon through 06Z tonight. Mainly VFR tonight outside of valley fog at LEB and possibly HIE and marine stratus/fog at RKD.

Outlook:

Friday-Saturday night: Generally VFR during the day with fog possible at night. Some brief MVFR restrictions are possible at coastal terminals Saturday if showers materialize.

Sunday-Sunday night: Generally MVFR conditions with widespread rain expected. Rain may taper off Sunday night giving way to areas of fog that would likely bring about IFR conditions.

Monday: Conditions return to VFR, but there may still be some MVFR and/or IFR conditions early.

MARINE

Through Tonight...SCA conditions are not expected. Winds briefly turn west, but remaining light, as weak boundary moves into the waters. Winds return to more southerly during the day as a weak front approaches, and these will switch to north/northwest tonight behind the front. Fog will also remain possible at times, especially from around Portland eastward.

Generally sub-SCA conditions are expected to prevail late week into early next week, but there is potential for a coastal system to bring some brief SCA conditions over the weekend. Areas of fog are also likely through much of this period.

GYX WATCHES/WARNINGS/ADVISORIES

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