An unseasonably cool airmass will creep into the region Monday morning and hang around through Tuesday behind this weekend's cold front. Here is a reason why you should wait until mid-May to plant many of your flower beds or your garden: Areas of frost and potentially sub-freezing temperatures will be possible in parts of the area.
- Forecast Surface Map Tuesday Morning (COD Models)
Here's the set up. High pressure will enter the region Monday and Tuesday making for clear skies and light winds. Temperatures aloft and humidity levels at the surface will also be quite low, allowing for the maximum potential for radiational cooling. At this point in time, the potential exists for portions of our area to see morning low temperatures Monday night into Tuesday morning in the 30's and possibly even 20's in the mountains.
- Forecast lows Tuesday morning (WeatherBell Models)
This will allow for some areas to develop frost around the D.C. Metro and potentially freezing conditions along and west of the Blue Ridge through the Shenandoah Valley. I have introduced that beautifully hand-drawn blue line to denote the freezing line, with temperatures forecast to be at or below freezing along and west of the line. This model does show, however, temperatures in the mid 30's closer to D.C. and upper 30's closer to the Chesapeake Bay. D.C. itself may see lows closer to the 40 degree mark.
Just how cold is this air compared to normal? The seasonal averages in D.C. for Tuesday are 75 degrees for the high temperature and 56 for the low temperature. Our current forecast is for a low in the low 40s inside the Beltway at Reagan National Airport, but that isn't far off from the record low of 41 degrees that day (the 14th).
- Tuesday Forecast Temperature Anomalies (WeatherBell Models)
Above is a look at the forecast temperature departures for the day across the Northeast. The region shaded in white and purple (which is a LARGE area) shows temperature anomalies at 15 degrees or more below normal. Some ares such as the darker purple shaded area over Western Maryland and parts of Pennsylvania and West Virginia even have the chance of seeing temperatures 20 degrees or more below normal. On a side note, the other side of the high which will experience the warm return flow could lead to temperatures in the upper 80s to near 90 degrees as far north as Minnesota!
Mike McGrath, WTOP's Garden Editor, tells Doug Hill and myself that it is best to typically wait until after May 15th to plant outside. This year that is no joke!
Big thanks to Bob Leffler for giving me the idea to write this blog. Thanks for the heads up!