Commissioning Week Weather Outlook (16 MAY 2018)

  POSTED ON: Wednesday, May 16, 2018 10:43 AM by METEOROLOGIST A.R. DAVIES

Executive Summary (Updated 18 May 2018 at 1430 EDT):

• Saturday: Seasonable with periods of steady rain during the day (80% chance). Off-and-on drizzle with scattered showers and thunderstorms in the evening/overnight (50% chance). East wind 8-13 mph.  High: 68-72 ^oF.
• Sunday: Partly sunny and warm with scattered showers and thunderstorms in the afternoon/evening (30% chance). Southwest wind 8-13 mph.  High: 78-82 ^oF.
• Monday: Partly sunny and warm with scattered showers/storms in the afternoon, evening, and overnight (40% chance). Variable wind around 5 mph. High: 78-82 ^oF.
• Tuesday: Partly cloudy with a chance for rain showers and thunderstorms (50% chance). Southeast wind 8-13 mph. High: 74-78 ^oF.
• Wednesday: Seasonable with a mix of clouds and sun. A slight chance for showers (30% chance). Low confidence forecast. West wind 5-10 mph. High: 74-78 ^oF.
• Thursday: Mostly sunny and pleasant. Northwest wind 8-13 mph. High: 76-80 ^oF.
• Friday: Partly sunny and seasonably mild. Slight chance for showers/storms in the evening/overnight (30% chance). Low forecast confidence. Northwest wind 5-10 mph. High: 78-82 ^oF.

Forecast Discussion (Posted 16 May 2018):

The rainy patterned that has gripped the Mid-Atlantic region this week shows no signs of letting up. Over the next ten days (through next Friday, May 25), the ECMWF (European Model) ensemble mean precipitation total in Annapolis is 5.0 to 6.0 inches (Figure below), with some individual models suggesting more rainfall is possible in isolated locations throughout Maryland. Probabilistically, the ECMWF ensemble models suggest an 80-90% chance of greater than 4.0 inches of rain over the next ten days with a 10-20% chance of greater than 8.0 inches.

A front has been unable to fully pass this week due to a strong area of high pressure off the U.S. East Coast. As a result, the front has taken a “semi-stalled” position (passing gradually to our north or south every few days) with waves of energy riding along it. This pattern will persist into the weekend as a non-tropical wave from the Gulf of Mexico lifts north along the front.  The large-scale southerly flow associated with the area of high pressure offshore will help the disturbance to pull ample moisture out of the Gulf/western Atlantic and into our region. As a result, expect periods of rain most of the day on Friday and Saturday (Figure below). There is some indication that the steady rain will depart Saturday evening (leaving only scattered showers), but that remains uncertain.  At this time, Sunday looks like the drier of the two days this weekend.

A cold front will approach the region on Monday afternoon, before passing on Tuesday.  Rain showers/thunderstorms seem likely Monday evening/overnight. With the strong area of high pressure still offshore, it is unclear how quickly the front will pass. If the front is slow moving or stalls (similar to what happened this week), showers and thunderstorms will still be possible on Tuesday, and perhaps even into Wednesday. However, at the moment the consensus forecast has the front to our south on Wednesday with a mix of clouds and sun (Figure below).

Another weather system will likely pass on Wednesday evening/Thursday with another round of rain. However, the last few runs of the GFS (American Model) and ECMWF (European Model) both suggest the system will be out of the area by Friday with gradually clearing skies. As shown below, the ECMWF ensemble model only suggests around a 20% of greater than 0.25 inches of rain on Friday (Figure below). Fingers crossed for good weather!

Category: General Interest