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Commissioning Week Weather Outlook (18 May 2016; Updated 19 May)

  POSTED ON: Wednesday, May 18, 2016 11:11 AM by Meteorologist A.R. Davies

Executive Summary: Commissioning Week Weather Outlook

  • Saturday: Cold and raw with periods of rain likely (90% chance). Rain could be heavy at times during the day. Northeast wind 10-15 mph, gusting to 25 mph. Low: 52-56 oF. High: 58-62 oF.
  • Sunday: Mostly cloudy with scattered showers (40% chance). North wind 8-12 mph. Low: 52-56 oF. High: 66-70 oF.
  • Monday: Partly cloudy with scatter showers (40% chance).  North wind 8-12 mph. Low: 54-58 oF. High: 66-70 oF.
  • Tuesday: Mix of clouds and sun. Rain showers possible (40% chance). Low confidence forecast. Northwest wind 5-10 mph. High: 64-68 oF.
  • Wednesday: Mix of clouds and sun. Rain showers possible (30% chance). Low confidence forecast.  West wind 5-10 mph. High: 68-72 oF.
  • Thursday: Partly sunny and warm.  Southwest wind 5-10 mph. High: 76-80 oF.
  • Friday: Mostly cloudy with a chance for light morning showers and sprinkles (30% chance). Steadier rain cloud develop in the afternoon/evening (45% chance). Increasing humidity. West wind d 8-12 mph. High: 76-80 oF.

The Commissioning Week Weather Outlook (above) was updated on May 19, 2016 at 1300 EDT. Continue to check www.usna.edu/weather for the latest information. Additional updates will periodically be posted at www.facebook.com/usnaweather.

Detailed Forecast Discussion:

A surface area of low pressure will slide across the Southeast United States on Friday afternoon, before pivoting northward Friday night/early Saturday morning.  As the system moves toward the Mid-Atlantic Coast, it will bring with it a significant slug of moisture from out of the Gulf of Mexico and off the Atlantic Ocean.  In addition, the surface feature will phase with a wave of energy in the upper atmosphere. As a result, periods of rain are likely throughout the day on Saturday.  Depending on the storm track, the rain could be heavy at times during the day. The figure below gives sense for the progression of the storm throughout the day on Saturday, along with how much rain could fall (bottom right).

Wx Forecast May 21 2016

Click here for a high resolution image.

Over the past 24 hours, the models seem to be slowly converging on a consensus forecast for Saturday; periods of steady rain are likely. However, there remains uncertainty as to how much rain will fall.  The latest operational, higher resolution model runs from the American/GFS model and the European/ECMWF model both suggest between 0.75 and 1.5 inches of total rain. However, some of ensemble models suggest as much as 2.0 inches. The local National Weather Service Office is officially forecasting 1.0 to 2.0 inches. There is also an indication over the last few model runs that the system will move out of the area a bit quicker with steady rain more likely during the day and tapering over in the evening. This trend will be worth watching over the next 24 to 48 hours.

A potential concern on Saturday will be the wind and wind direction. Depending on the storm track and how quickly the system departs, sustained easterly winds 10-15 mph (gusts to 25 mph) are possible on Saturday.  This may result in minor coastal flooding (nuisance flooding around the Yard), particularly if steady rain falls on our already saturated ground.

Going into next week, the pesky upper atmospheric wave of energy will likely linger over the East Coast through Tuesday, with rain chances almost every day.  Monday morning should be rain-free, but atmospheric instability resulting for the upper air energy could result in scattered afternoon/evening pop-up showers with isolated thunderstorms.  By Tuesday, both the European and American models suggest that the upper level wave will manifest itself at the surface as substantial weather system off the Mid Atlantic coast. At this time, the storm track and development of this system is uncertain because it is expected to retrograde (i.e. move east to west, instead of the normal west to east storm motion) and come ashore sometime on Tuesday/Tuesday night. The models have historically preformed sub-par with this type of situation, particularly 5+ days out.  The figure below shows the approximate storm location at 0800 EDT on Tuesday, along with the potential storm tracks.

Precip and MSL on 24 May 2016

Click here for a high resolution image.

Depending on how the offshore system behaves, Tuesday or Wednesday could be windy/rain, sunny/calm, or something in between. My best guess at this time would be that Tuesday (particularly Tuesday evening) presents the best chance for steadier rain, with the system departing by mid-morning on Wednesday (perhaps even some clearing Wednesday afternoon/evening). I also do not anticipate a total wash out either day.  However, clouds will also be a concern for the Blue Angles on Tuesday (practice) and Wednesday (show).  As shown in the figure below, even if the system remains well offshore, the cloud deck could extend inland and over Annapolis Tuesday or Wednesday (storm track dependent).  It remains too early to know for sure, but something worth watching.

Sat simulation on 24 May 2016

Click here for a high resolution image.

A slow moving frontal system will try to push through late next week. The latest model runs suggest that the system will arrive later in the day on Friday (although overall forecast confidence remains low).  If the pattern develops this way, Thursday, May 26 could be wedged between two weather systems and may end up being the best day of the week with partly sunny skies, light southerly flow, and a high temperature in the upper 70’s or near 80 degrees.  The southerly flow could also result in a bump in the humidity late in the week. The latest runs of both the American and European operational models suggest that the next weather system may hold-off until Friday afternoon.  The figure below shows the projected weather pattern at 0800 EDT on May 27.

Precip and MSLP on 27 May 2016

Click here for a high resolution image.

In this projection from the American model, most of the rain is west of Annapolis and across the Ohio River Valley on Friday morning.  If this model projection holds, a few passing sprinkles or showers may be possible through midday on Friday before steadier rain perhaps arrives later in the afternoon.  While it is still too early to tell exactly how this system will develop/impact us, it is important to note there is a chance for rain showers next Friday.  One positive development is that the GEFS Ensemble Models suggest a similar pattern as the operational American/GFS model (shown above).  From a probabilistic forecasting perspective, this suggests a modest degree confidence in the American model forecast for next Friday.  This is encouraging because forecast confidence is already low 10 days out.  Furthermore, as shown in the figure below from the GEFS Ensemble Model, the probability of >0.25 inches of rain between 1400 EDT on May 26 and 1400 EDT on May 27 is low (<20% chance). Fingers Crossed!

Precent Changes of Precip 26 to 27 May 2016

Click here for high resolution image.

ISSUED: 18 May 2016 at 1100
FORECASTER: Meteorologist A.R. Davies
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Disclaimer: This is not an official U.S. Navy weather forecast and should not be confused with the official Navy weather forecast provided by the Fleet Weather Center in Norfolk, VA.  Furthermore, the official U.S. Government forecast for the greater Annapolis area is issued by the National Weather Service Baltimore/Washington Forecast Office in Sterling, VA. Click here for full disclaimer.

Category: General Interest

Contact:

Alexnader R. Davies
Meteorologist & Oceanographer
Oceanography Department, USNA
  adavies@usna.edu
  410-293-6565