textproduct: Gray - Portland

WHAT HAS CHANGED

Rainfall amounts have trended upwards for the late Monday into Tuesday system. These trends will have to be watched closely for potential flood risks.

KEY MESSAGES

1. Scattered showers and storms diminish by sunset this evening. Slow moving storms have produced heavy rainfall and a localized risk for flash flooding.

2. Low pressure crosses late Monday into Tuesday morning bringing widespread rainfall. A swath of heavy rainfall is possible with this system bringing the risk of flooding.

3. Weather is likely to remain unsettled through the rest of next week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Latest radar shows scattered thunderstorms across Maine and New Hampshire with these storms having a history of producing rainfall rates of 1-2 inches per hour. Ample CAPE across the area has allowed for some stronger cells to contain small hail while the lack of shear has largely keep storms sub-severe. Scattered storms will continue into this evening and will wane with the loss of heating. The primary hazard with these storms will be localized heavy rainfall and possibly the need for additional flash flood warnings.

KEY MESSAGE 2 DESCRIPTION...

Mesoscale models are in decent agreement in an area of low pressure tracking across southern New England late Monday into Tuesday morning bringing a swath of moderate to heavy rainfall across the area. On the other hand, global models and their ensembles (mainly the GEFS) still have several members that keep the heaviest rainfall to the south of the forecast area. These southern track ensemble members are likely holding down the NBM QPF forecast and could see rainfall amounts trend higher over the next forecast cycle if the agreement amongst mesoscale models continues.

The synoptic setup is not overly impressive with a low amplitude wave emerging from the Ohio Valley that partially phases with an upper low over SE Canada. There is a signal for the right entrance region of the upper jet to be near by and this could aid in synoptic ascent. Most model solutions bring a plume of PWATs nearing 1.75 inches across souther areas with PWATs greater than 2 inches close by. Ultimately, the variability in rainfall amounts will hinge on how far north the low tracks that will allow for higher PWATs into the area along with better instability. Warm cloud depths nearing 12kFT will also aid in rainfall efficiency. The latest HREF does raise some concerns the mean QPF of 2-3 inches across central NH into the White Mountains extending into the foothills of western Maine. The HREF max QPF brings amounts up to 5 inches in these same areas. Therefore, stay tune to the latest forecast updates because these higher end amounts will likely warrant a Flood Watch.

Low pressure exits Tuesday late Tuesday morning with a drying trend into Tuesday afternoon.

KEY MESSAGE 3 DESCRIPTION...

A relatively zonal mid-level pattern is likely through the end of this week. This will allow for the potential to see routine bouts of unsettled weather by Thursday and Friday across northern New England.

Through the second half of the week, instability over the area is likely to generate scattered showers and thunderstorms. Temperatures also look a little warmer, with high temperatures in the upper 70s and lower 80s through the rest of the week. Wednesday has the best chance to be the driest day of the three, with scattered thunderstorms appearing more likely for Thursday and Friday.

AVIATION /00Z MONDAY THROUGH FRIDAY/

A few lingering showers remain and are weakening with time, but very localized MVFR conditions possible from AUG-WVL to the coast until then. Otherwise VFR conditions thru about midnight and then radiation fog is anticipated tonight. Local IFR or lower possible and chances will be higher in locations where it rained earlier today. Confidence is highest at LEB and HIE, but it may also include AUG, RKD, PWM, and CON. Conditions return to VFR around sunrise, with conditions again deteriorating in the evening. Areas of MVFR or lower are likely as widespread rainfall moves into the region.

Outlook:

Monday night-Tuesday: IFR likely Monday night into Tuesday morning in low cigs and rain. Conditions improve into Tuesday afternoon.

Wednesday: Mainly VFR.

Thursday-Friday: Showers bring potential for restrictions.

MARINE

Winds and seas remain below SCA thresholds through Monday. Low pressure crossing southern New England will bring increasing south winds approaching 25 kts Tuesday morning. Winds shift offshore Tuesday afternoon with winds and seas largely remaining below SCA thresholds through late week.

GYX WATCHES/WARNINGS/ADVISORIES

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