Daily Discussion [6/17] Flood Watch, Severe Storms, Oh My!


  • Showers this AM along frontal boundary
  • Flash flood watch issued for today
  • Afternoon storms building around 2 PM
  • Some storms may turn severe; primarily Allentown on south

Surface Analysis

We have a boundary sitting right through Pennsylvania today. As explained yesterday and in the short term outlook on 6/15, this front will be the focus of several storm passages through the week.


Click for latest Composite Reflectivity radar image from the Mt. Holly, NJ radar and current weather warnings

Showers moving through the area along a warm front. These will persist through the early morning and lift NE’ward.

Regional satellite showing clearing to the south and west. There will be some sunshine today.

Temp and Precip Outlook

High temperatures today will be in the low 80s for much of the area, a little cooler down the shore with temps staying in the 70s.

Most of the area is expected to receive over an 1″ of rain through tomorrow morning. This map does include the morning showers. Of course, the better the thunderstorm formation, the higher likelihood areas exceed 1″ of rain. There is an isolated location in the Lehigh Valley that is expected to exceed 1.5″ of rain and that is due to the rejuvenated showers this AM. Tomorrow morning another batch of precip will make its way from W. Pa into C. Pa, also increasing precip totals.

Thunderstorm Outlook

We have a slight risk issued for Philadelphia on south, meaning there is a chance for scattered thunderstorm activity, with some storms turning severe. As was the case yesterday, hail and damaging winds are the primary severe threat. Flash flooding is the greatest concern given the already saturated grounds.

NAM For This Evening

Weak surface low develops to the south, but that’s more than enough to initiate convection.

And the precip persists until late tonight/midnight.

Wide View look for tonight at 6PM shows our thunderstorms but also shows next batch of precip in Indiana that will create heavy rain tomorrow morning for W. Pa and C. Pa.

Further Discussion

12z NAM just rolling in shows fair amount of CAPE, approaching 2000 J/kg. The mid-level lapse rates are on the lower side, but the lifted index is moderate at -5 at the surface. There is some directional sheer, particularly at the lower levels, so isolated tornado chance cannot be ruled out. Still, the convective nature will be limited due to the column temp and there will also be little “cap” to allow low level convective elements to build and then explode like you see with widespread severe outbreak. Still, there will be a vigorous shortwave trough that will act like its own lifting mechanism.

Soundings are in agreement with slight tornado potential, if all things come together perfectly. The chances are limited, but they are there.

Radar and more: College of DuPage

Mesoanalysis: https://www.spc.noaa.gov/exper/mesoanalysis/new/viewsector.php?sector=16#

CAPE? Shear? What?!? Severe Weather Terms: https://www.spc.noaa.gov/sfctest/help/sfcoa.html

Latest text updates from SPC: https://www.spc.noaa.gov/

Local Warnings and Statements NWS Mt. Holly: https://www.weather.gov/phi/

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