textproduct: Raleigh

WHAT HAS CHANGED

* No significant changes to earlier forecasts.

KEY MESSAGES

As of 300 PM Tuesday...

1) Isolated to scattered storms may produce pockets of heavy rainfall through this evening.

2) A pair of cold fronts will bring another chance of showers and storms on Thursday. A drier period will follow, with the exception of Saturday when another cold front moves through.

DISCUSSION

As of 300 PM Tuesday...

KEY MESSAGE 1... Isolated to scattered storms may produce pockets of heavy rainfall through this evening.

As noted in previous discussions, the potential for pockets of locally heavy rainfall persists today through this evening, albeit a slightly lower threat than yesterday. We remain in a high-PW environment (values 150-180% of normal streaming N/NE around the periphery of the offshore-centered mid level ridge), with a deep warm layer (LCL-to-0C height of 3.6-3.9 km). Faster SSW 850 mb flow is also contributing to lower MBE motion and modest movement of convective clusters, amidst widespread moderate skinny SBCAPE. All of this supports maintenance of high coverage of showers and embedded storms capable of fairly high rain rates, with 0.5- 1.0"/hour common, and some areas that see training cells could see 1- 2" rates and 2-3" storm totals. The earlier hi-res model runs from yesterday and last night didn't do too well in pinpointing the location of the showers and storms out there now, but the 12z HREF LPMM has caught up somewhat in showing the highest coverage in the far NE and in the SW half, with a 50-70% probability of 1" in 3 hrs over the S and SE CWA through the afternoon and just NW of the area this evening, with chances lower at 30-50% in between. We're still under the influence of very weak/subtle mid level perturbations and MCVs riding N/NNE from the E Gulf Coast to help add dynamic forcing for ascent, although we're farther removed from the upper jet right entrance region compared to yesterday, so coverage of the heavier precip is likely to be a bit lower today than on Mon. Nevertheless, with the rates we're seeing so far, a few flood advisories may be needed, especially in those areas that saw an inch or more Mon. Convection is expected to dwindle after midnight.

By Wed, the mid level ridge will flatten out over NC in response to a diving shortwave trough into the N Great Lakes/St Lawrence, on the east side of the omega block. This will result in a veering of low- to-mid-level flow to more westerly over NC and a reduction in PW as the higher/deeper moisture is shunted to our S. So while there will still be above-normal chances for showers and scattered storms, the risk for locally heavy rainfall will be lower.

KEY MESSAGE 2... A pair of cold fronts will bring another chance of showers and storms on Thursday. A drier period will follow, with the exception of Saturday when another cold front moves through.

A closed mid/upper low over the Canadian Maritimes will result in weak mid-level height falls over central NC on Thursday. It will also drop a couple of cold fronts south through our region, one on Thursday and another on Thursday night. The first front may be associated with a decaying line of convection across our northern zones on Thursday morning which could reignite heavier showers and storms in the south during the afternoon. However, given that we will be on the backside of the trough and the mean flow will be westerly then northwesterly, PW values will be lower than previous days (around 100-125% of normal). So convective coverage should be lower as well, mainly isolated to scattered in nature and focused mostly in the south where the best moisture and instability will be. Thus excessive rainfall is less of a concern. Dry weather is expected Thursday night and Friday as surface high pressure builds in from the Great Lakes.

The next chance for showers and storms comes Friday night and Saturday as the stalled boundary to our south tries to lift slightly north and a wave of low pressure rides along it. The main threat for heavy rain would be across our southern zones, but even here confidence is low as it will depend on how far north the low is able to get, and the best moisture/instability will again be to our south. Meanwhile another low pressure system tracking across and offshore New England will drop a backdoor cold front through central NC on Saturday or Saturday night. This will mostly put an end to our rain chances, with much drier weather from Sunday into early next week under the influence of NW flow aloft as we remain on the backside of troughing over the North Atlantic. Still can't rule out an isolated shower or storm each day with disturbances rotating around the trough.

We will have one last warm and fairly humid day on Thursday with highs in the lower-80s to 90 and dew points in the mid-to-upper-60s. Conditions will then turn much more comfortable on Friday as highs reach the upper-70s to lower-80s and dew points drop into the 50s. We then turn cooler than normal from Saturday to Tuesday with highs in the mid-70s to lower-80s and lows in the 50s.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

As of 750 PM Monday...

The showers/storms have generally weakened to light showers or sprinkles. Therefore, generally VFR conditions are expected through 05z-07z before low stratus develops. Low stratus (IFR) conditions are expected between 08z and 14z before lifting out to VFR conditions by late morning Wednesday. There is a chance of a shower or storm during the afternoon/evening Wednesday, but the chances will be much lower than the last few days as a drier WNW flow aloft begins Wednesday afternoon and night.

Looking beyond 00z Thursday, A surface cold front will move south through the region early Thursday. VFR conditions will prevail late week with the drier northerly surface flow. The next chance of showers should be Friday night into Saturday as low pressure possibly tracks to our south, with the best chance of showers over southern NC.

CLIMATE

Record High Minimum Temperatures:

May 26: KGSO: 70/2019 KRDU: 73/2011 KFAY: 75/2004

May 27: KGSO: 72/1991 KRDU: 72/1991 KFAY: 72/2006

May 28: KGSO: 70/2012 KRDU: 74/1914

RAH WATCHES/WARNINGS/ADVISORIES

None.