textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes with this forecast update.

KEY MESSAGES

1. Wet weather continues through midday to early afternoon. Much warmer with a chance of showers late Tuesday.

2. A fairly unsettled but 2nd half of the week is expected, with cooler temperatures and scattered showers likely. The weekend continues to look unsettled as well.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

First round of showers continues to drift east, but the forecast area is going to remain in a region of warm advection through morning. That will not be enough to dislodge the cooler surface air, so I anticipate that even if it is not raining per se there will be plenty of drizzle and perhaps some fog near the coast. But the next round of rain is already taking shape across New York and Pennsylvania ahead of the cold front. As opposed to the light rain experienced so far, these rainfall rates will be more convective and some moderate rates are already being observed across central New York. Very early this morning as warm advection is strongest, there will be some elevated instability developing. Up to a couple hundred J/kg CAPE is forecast, so I believe that briefly heavy rainfall rates are possible. As a result the next 12ish hours of QPF has bumped up a bit on modeling. HREF guidance now has a mean QPF thru this evening of 1 to 1.5 inches. The max QPF in that time is not much higher, so it would appear CAM guidance is all fairly consistent with a good slug of rainfall. Currently forecasts also have this moving rather quickly thru the area, wrapping up by midday in the west and early afternoon farther east.

Things will turn much warmer by Tue. A return to widespread 70s and 80s is likely ahead of the next shortwave trof. That is forecast to arrive late across the region, bringing another chance of showers and thunderstorms. Right now this is mainly a threat for the northern half of the forecast area, but we will have to watch the timing on that. If the front can speed up closer to peak heating, forecast soundings indicate some skinny CAPE, good mid level dry air, and strong mid level winds. Some of those storms could end up bringing some gusty winds.

KEY MESSAGE 2 DESCRIPTION...

Tuesday night a short wave trough will move in from the northwest with increasing chances for showers in the north with isolated thunder not totally out of the question. Wednesday will be a bit cooler but still pretty warm. Heights will continue to fall on Wednesday and this will likely aid in scattered showers but it will not a washout by any means.

Various sources of guidance begin to diverge with respect to the upper air pattern over Quebec on Thursday. Most ensemble guidance shows upper level low pressure diving into New England sometime between later Thursday and Saturday. This will likely portend to unsettled weather. However, timing and amplitude has to come into better agreement for us to have more confidence in the late week and weekend forecast which could be wet at times.

AVIATION /00Z MONDAY THROUGH FRIDAY/

Through 06z Tuesday...Conditions continue to deteriorate despite dry slot pushing into the region. The expectation is for CIGs to continue to lower and expand up to the southeast slopes of the mtns thru the morning so that widespread IFR or lower exists by sunrise. Some fog may develop near the coast even with the diminishing threat of showers. I can't rule out a rumble of thunder as more rain/showers develop towards early morning, but confidence is low enough to not include in the TAFs at this time. Rain may be briefly heavy at times and reduce visibility locally elsewhere. After that rainfall moves thru the area we will see gradual improvement early to mid afternoon but some MVFR CIGs will likely stubbornly hang around. By late afternoon, most sites should improve to VFR categories but some lingering MVFR is possible in the mtns, potentially impacting HIE.

Outlook:

Tuesday: VFR conditions expected. Some local MVFR or lower possible around HIE in showers late.

Tuesday night: Local MVFR possible in the mtns with showers and isolated thunder possible early.

Wednesday: MVFR possible due to sct showers and possible isold thunder.

Wednesday night: MVFR possible due to showers.

Thursday: MVFR possible due to showers.

Friday: MVFR possible due to showers.

MARINE

SCA remains in effect for seas building to 5 or 6 feet on the coastal waters. Winds may briefly gust to near 25 kt, but overall expect those to remain below SCA thresholds. Some areas of fog will be possible thru midday before winds shift to offshore and clear out the low level moisture. Winds and seas will diminish tonight. Small craft conditions are not currently anticipated Tuesday night through Friday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory from 2 AM Monday to 8 AM EDT Tuesday for ANZ150-152-154.