CAPE

Wow what a great technical discussion from WPC- MESOSCALE PRECIPITATION DISCUSSION 0515...CORRECTED NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 612 PM EDT SUN JUL 22 2018 CORRECTED FOR FLASH FLOODING LIKELY IN CONCERNING LINE AREAS AFFECTED...SOUTHEAST PA...CENTRAL MD...EXT NORTHERN VA...EXT NORTHERN DE... CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY VALID 222158Z - 230145Z SUMMARY...A COUPLE OF COMPLEXES FED BY SWLY ONSHORE FLOW FOCUSED BY RIVERS POSE LIKELY FLASH FLOODING ACROSS SE PA TO CENTRAL MD OVER THE NEXT FEW HOURS. DISCUSSION...MCV LIFTING INTO CENTRAL PA CONTINUES TO HAVE AN ACTIVE CONVECTIVE COMPLEX ALONG THE EASTERN PERIPHERY OF ITS INFLUENCE IN SE PA/EXT NE MD AND N DE ATTM. STRONG SFC FLOW UP THE DELAWARE RIVER AND SLIGHT TURNING AT THE APEX OF THE CHESAPEAKE BAY LEADING TO VERY STRONG MST CONVERGENCE AND BACKBUILDING GIVEN STRONGER INFLOW AT THE EDGE OF THE MID-LEVEL TROF/CONFLUENCE BAND. THIS ALSO INTERSECTS GENERALLY WITH THE WARM FRONT THAT CONTINUES HANG THROUGH SE PA INTO ANNE ARUNDEL COUNTY MD INTO THE PIEDMONT REGION OF VA. STRONG MST CONVERGENCE ALONG THE WARM FRONT IS SUPPORTING CONVECTIVE DEVELOPMENT ALONG ITS LENGTH INTO VA BUT GIVEN THE STUBBORN NATURE OF THE RIDGING OVER WEST CENTRAL MD INTO NW VA...THERE CONTINUES TO BE SLOW NNW MOVEMENT OF THE FRONT ALLOWING FOR BACKBUILDING ALONG THE UPSTREAM EDGE AND COMPOUNDING RAINFALL TOTALS DOWNSTREAM. THE BEST TRAINING REMAINS WHERE THE FRONT IS MORE PARALLEL TO THE MEAN FLOW ACROSS SOUTHERN MD TOWARD BALTIMORE CITY. IN ADDITION ANOTHER SUBTLE S/W WILL HAS INCREASED WAA ACROSS THE NORTHERN NECK OF VA LIFTING NORTH SUPPORTING A BAND OF CONVECTION THAT WILL LIKELY BE ENHANCED BY THIS PARALLEL NATURE TO THE FRONT AND THE INCREASED LOW LEVEL FLUX/CONVERGENCE CONTINUING THE FLASH FLOOD THREAT FOR THE NEXT FEW HOURS ALONG THE LENGTH OF THE CHESAPEAKE BAY.

Could be a weak impulse, but a more impressive one looks to swing through tomorrow. There is also a stationary boundary lying SW to NE from southern MD to SE PA associated with the action today, so that may continue to serve as a focus for any convection that occurs overnight, although it will probably be weaker due to loss of insolation.

Looks like either side of the bay got hit hard today. Multiple rounds of storms over the same areas. Makes sense given the location of the vort max moving through just to the west over central VA/MD as advertised by the meso models early this morning. Probably some bay breeze contribution at the lower levels as well.

Just a parade of vorticity impulses moving through over the next 48 hours on the NAM. Looks like as the closed low sinks a bit south and east, the track of the vort maxes/associated enhanced lift, and thus the threat for heavy rain, will shift/expand a bit further east tomorrow. Round 4 today just missed here again. Pretty amazing looking at the storm totals per radar for today. A north-south axis of 2-4 inches through Talbot and Queen Annes counties a few miles to my west, and nothing here.

3 rounds of storms today have tracked S to N a few miles west of me. Had literally a few drops all day. This next one seems to have a bit different orientation, so maybe I get clipped. Or maybe it dies before it gets here lol. Lots of rumbling to my south.

That little shortwave (vorticity max) moving N-NW from central VA is going to be a trigger for heavy rain today, along with any localized low level forcing mechanisms.

Been quite sunny here this morning, except when that line a few miles west of here passed by, but back to mostly sunny now. In general the location of the upper low to the west and the blocking ridge to the east are going to dictate where any minor upper level perturbations might track and contribute to heavy rain potential- and it looks like it is favored to be over the same areas that got crushed yesterday.

Yeah I am pretty much right in the middle between the moderate and slight contours. Those products are not meant to be precise, and as we saw yesterday they continually update based on latest trends. That being said, I just missed that heavy line of showers that developed just to my SW in the last hour- it moved N and slightly NW. Seems most of the action will be to my west today.

Nice line of storms developed right over route 50 between Wye Mills and Cambridge.

Man just brutal. Be glad its July and not January.

Just a measly 2.48" here. After 3+ weeks of ignoring my burning lawn, I suppose its now time to think about mowing the weeds and any surviving grass.

This event is cool because it is pretty darn uncommon to get a (non tropical) low tracking up the east coast in mid summer producing widespread heavy rain and relatively cool temps. This has been a fall-like storm. The rest of the week should also be fun, with several perturbations moving through with a deep southerly flow between the blocking atlantic ridge and the trough/upper low just to the west. Much more summer like with high dews and chances for convection. Quite a few places in the area should see totals the next few days exceed what fell today.

2.03" so far. Looks like it might be winding down here. Sort of in a dry slot, although still some showers rotating through, but nothing heavy. Sucks Dover radar is offline(it is way too often during actual events) which makes it a bit difficult to see whats happening. It was pouring earlier, and looking at both Sterling and Mt Holly radar, it looked like drizzle here lol.

Yeah it nailed the potential. But then it moved axis of heaviest precip from east of the bay, to over the bay, to the DC area, points west...then moved it back towards Annapolis and the bay, then back west again. Because it changes every hour, it usually ends up nailing something. Love the HRRR!

Just hit 1.5" here. Its lightened up a bit but it was torrential with some decent wind for a while.

lol the HRRR 16z has it over the bay.

Nice downpour here now. Winds picking up some too. Feels a tad raw out. 0.65" in the bucket.

Fixed.

Looks like the main show has arrived here. Moderate to heavy rain. Will be interesting to see how much wind materializes later.

Been getting some light to moderate rain here the past hour. Was hoping this would hold off till noon. Oh well, guess I will stay inside and move happy hour up 4 hours or so.

FF watch for MD eastern shore, all of DE and southern half of NJ. Forecast for mby is 2-4" through tomorrow night. Bring it. Way too late to save my torched grass though. I guess I will be doing the annual re-seed in another month.

Cool read from Mt Holly AFD.. A high amplitude pattern will feature a cutoff low over the Midwest that is sandwiched between strong downstream ridging over the western Atlantic basin as well as an anticyclone over the Southwest U.S. and Southern Plains. As mentioned in the previous section, a secondary low will organize near the base of the negatively-tilted trough in coastal Carolinas tonight. This coastal low is then forecast to continue deepening to around 1004 mb on Saturday as it tracks northward toward the Delmarva. Models continue to show a well- developed mid-latitude cyclone as it moves into our area later in the day, which is rather extraordinary for the middle of summer. Low CAPE profiles from the latest models indicate a rather low threat of lightning without the presence of upright convective instability to support deeper updrafts. However, cross-sectional analysis from the 12Z NAM and GFS show the potential for CSI along and east of the low track where very high theta-e air in the warm sector wraps around the low. Accordingly, the potential for slantwise instability juxtaposed in a region of very strong lift from an impressive 60-kt SEly low-level jet (zonal and meridional component wind anomalies of -5SD and +5SD, respectively) and deep tropical moisture (forecast PWATs of 2.25-2.5" would be near-record values) will be more than enough to compensate for a lack of upright instability to produce heavy rainfall rates in excess of 1-2" per hour.

From Mount Holly morning AFD- Saturday and Saturday night...The coastal low will start to make its way up the coast on Saturday. The models continue to have differences with respect to timing, strength, and speed of the low as it moves up the coast but the solutions again look closer than they did on their previous runs. The models have all shifted slightly west with the track of the low, with it hugging the coastline. All of the guidance continues to suggest heavy rainfall with the low as it moves across the region. WPC has put us in a slight risk for excessive rainfall and we agree. Hi-res models and the deterministic models show 2-5+ inches in some areas through Saturday. However, with the exact track and timing (GFS is fast, NAM is slower, and ECMWF is slower still) still a bit uncertain, it is hard to pinpoint just which areas are the most at risk for the higher rainfall totals. Flash flooding is a concern and although we have had a dry period of late, the rain will fall quickly and will not be as easily absorbed into the ground. A Flash Flood Watch may be needed as the details become a little clearer based on later model runs today.

lol

Euro total precip Sat through Tuesday.