[10gigs] NWS forecast discussion

[Jon Platt]

Mpls NWS discussion regarding the weekend:  (WWA = warm air advection)


A pseudo-stationary boundary will enter the region today and will be the locus of what will be multiple rounds of showers and storms over the weekend, with the location of the boundary going to be a key focal point of the forecast in terms of where the heaviest rainfall will end up.
Heat and humidity will build today ahead of a plume of lower mid level warm air and moisture that will arrive with the boundary later today, with heat indices peaking in the mid to upper 90s this afternoon and again tomorrow afternoon. We may see a brief hour or two of heat indices exceeding heat advisory criteria, however the duration for now looks to be short enough such that an advisory may not be needed, especially if cloud cover and convective debris end up knocking down the high temperatures just a bit. Ensemble guidance shows a fairly high likelihood of highs in the upper 80s for a large portion of the MPX CWA, with dew points increasing into the mid 70s within the primary warm air advection zone south of the boundary. Right now, there is still not a clear consensus within the suite of guidance to pinpoint the location of the boundary, however for now it looks to favor near or north of the Twin Cities which would place most of the CWA within the WAA zone. Potential for severe weather will largely be confined to the immediate area near the boundary as shear will be locally maximized, however a lower-mid level cap as well as high PWATs are making this event seem more like a flooding threat than a large scale severe weather threat. CFSR climatology from the ECMWF shows a plume of 99th or higher percentile PWATs over a large portion of the area beginning this evening and continuing through Tuesday morning, with both the CFSR ECMWF and NAEFS showing PWATS in excess of 2 inches for the next few nights. There is high confidence in significant moisture being present with the highest overall areal coverage in terms of the percentiles being Sunday night into Monday morning after a few days of consistent low level WAA and moisture advection take place. Stay tuned for further details including the location of the boundary and most likely area for localized flooding as we see more CAMs come into play that will capture the full event over the next 24-36 hours.


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