BBS: TELESC.NET.BR Assunto: HVYRAIN: Excessive Rainfall Discussion De: COD Weather Processor Data: Sun, 15 Mar 2026 07:44:04 +0000 ----------------------------------------------------------- FOUS30 KWBC 150743 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 343 AM EDT Sun Mar 15 2026 Day 1 Valid 12Z Sun Mar 15 2026 - 12Z Mon Mar 16 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHEAST PENINSULAR FLORIDA... A very strong dynamic cyclone will be in full force across the Upper Midwest and Upper Great Lakes with a strong attendant cold front crossing out of the Plains through the Lower Ohio and Mississippi Valley. The strength of the low level flow prior to the cold front will draw modest moisture through the Valleys to provide 1-1.25" Total PWat values. The focus will be on severe aspects of the convective line and there will be some stronger updrafts and=20 solid moisture flux convergence associated with these convective=20 cores capable of sub-hourly to hourly rates/totals in the vicinity of 1-1.5"; the duration will be brief to limit overall totals to less than 2" overall. This could result in random, widely spaced incident or two of flash flooding, but limited to urban and traditionally flood prone locations. So while there is a non-zero risk of excessive rainfall, it remains below the 5% coverage for a Marginal Risk to be delineated at this time but will continue to monitor trends for subsequent updates.=20 Further southeast, the draw of moisture out of the Caribbean through the Strait of Yucatan will draw higher moisture though the eastern Gulf. Combined with return easterly flow north of the Greater Antilles into the Bahamas; there is an increase in=20 moisture confluence (total PWats to 1.75") through Peninsular=20 Florida. Onshore flow from the southeast and clearing skies will=20 allow for some increased instability (1250-1500 J/kg) to build for=20 thunderstorm activity across the southern Peninsula before evening. Rates in excess of 2"/hr may result in highly localized spots of=20 2-5" that may result in localized rapid inundation flooding if over the southern I-95 urban corridor. Converging sea-breezes may also=20 result in mergers across the central Peninsula from north to south, but are likely to be more intense initially but also much more=20 brief relative to those closer to coastal convergence zones that=20 may allow for longer duration. HREF probabilities of 3-5"/24hrs are sufficient to highlight a small Marginal Risk of Excessive=20 Rainfall.=20 Gallina Day 2 Valid 12Z Mon Mar 16 2026 - 12Z Tue Mar 17 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID-ATLANTIC AND NORTHEASTERN U.S & EXTREME NORTHWEST WASHINGTON... ...Mid-Atlantic into Northeast... Highly meridional moisture surge will be already ongoing at the start of the forecast period (16.12z) as the leading edge of the Atlantic warm front should be lifting through southern New England and Gulf of Maine. Upstream the highly dynamic cyclone will be well occluded through depth across the north-central Great Lakes with a powerful near 980mb surface low and attendant sharp cold front extending due south across the Mid-Ohio Valley, Cumberland Plateau into the central Deep South. The based of the large scale trough will be lifting northeastward providing solid dPVA to support strengthening deep layer southerly flow further compounding on the initial warm advective surge through out of the Southeast through the Mid-Atlantic. Integrated Vapor Transport (IVT) values will=20 increase from upper hundreds of kg/m/s toward 1250 kg/m/s across=20 the Coastal Plain into southern New England eventually reaching=20 values over 1400 kg/m/s after 00z through S ME due to the combining strength of the LLJ and confluent moisture streams off the Eastern Gulf and Western Atlantic. This brings moisture flux well above=20 97-99th+ percentiles of moisture flux. Instability will be a=20 limiting factor for vertical development along/ahead of the cold=20 front but some 250-750 J/kg will be available through the central=20 Mid- Atlantic with some localized convergence for scattered showers and thunderstorms prior to the main cold front/squall line to=20 emerge out of the Appalachian terrain by mid-day. These initial=20 cells should be quick moving and limited in total, but any that=20 broaden into stronger isolated super-cells may have capability for=20 locally intense rates prior to the main line. Still, the main focus will be the hourly to sub- hourly 1-1.5+" totals with the main=20 convective line that will have greatest potential for localized,=20 mainly minor flash flooding impacts. Hydrologically, the Northeast remains highly saturated and cold through depth with modest SWE in some remaining snow pack. So, while the rain rates will likely be much lower due to lack of deep unstable/vertical shower activity; the orographic ascent and should remain concerning that any rain on snow will further compound the ongoing hydrologic/stream rises (please refer to National Water Center FHO and Local River Forecast Center forecasts for further river concerns across this region). As such a broad Marginal Risk will remain in place for nearly all=20 of the Northeast (minus areas in south to south-southwest rain=20 shadow areas of far N VT), with an extension of the Marginal into=20 the Potomac River Valley and southern extents of the Megalopolis=20 where those higher rates/short-burst totals may result with=20 localized exceedance of lower hourly FFG values.=20 ...Pacific Northwest... Prolonged warm advection of a moderate positively anomalous moisture stream will be continuing across the extreme northwestern portion of the Olympic Peninsula with a very weak continuation to the northern Washington Cascades. Rates will remain fairly consistent between .25"-.33"/hr allowing for totals to near 3-5" toward the the end of the forecast period with 00z HREF probability of 5" nearing 30%; though 5"/24hr just across the Sound will be near 60%. By late evening/early overnight period, the cold front will be starting to surge southeastward and further direct enhanced moisture flux toward the Olympic Peninsula after 06z, with 1-1.25" Total PWats fluxed on 40-45kts of flow generally resulting in about 750 kg/m/s IVT values, bringing rates locally up to .5" for the best orographic ascent regions. As such, a very small Marginal Risk was included for this AR surge into an area already at above=20 average soil saturation due to recent AR plumes in the last few days/week(s).=20 Gallina Day 3 Valid 12Z Tue Mar 17 2026 - 12Z Wed Mar 18 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF NORTHWEST WASHINGTON... At the start of the day 3 forecast period, 18.12z, the strong, prolonged Atmospheric River had recently shifted slightly eastward directing the core of the AR plume centered across Northwest Washington into the northern Cascades, oriented from SW to NE. Deep layer moisture remained well above normal with total PWat values remaining well above 1" with 1.25" reaching the southwest flanks of the Olympic Range. Winds had calmed a tad but remain around or above 40kts through the 850-700mb range favorably orthogonal to the Olympic Range. Freezing levels are well above even the highest peaks, exposing some Snow Water Equivalent (SWE) to the higher WAA southwesterly flow adding to the .25"-.33"/hr rain rates though=20 will be higher earlier in the period as winds slack ever so subtly=20 between shortwave features. Overall IVT values will remain above=20 500 kg/m/s with peak values over 750 that extend into the northern=20 Cascades as well. As such, 24hr totals will once again be over 3-4" and combined with the snow melt, could further increase stream=20 flows. With lower rates, a Marginal Risk of Excessive Rainfall will remain in place; however, please refer the National Water Center=20 and NWRFC forecasts for stream/river flow/rise information with=20 respect to increasing flooding potential.=20 Gallina Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4AzIGu5_fSSFHHo4mH424lnBHY9KVSHK94fpyMy9ry8V= hqiV1vTtMG0fms-pMqlJ6Pzo-szMpgzciOPiBYt1SmikUJ0$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4AzIGu5_fSSFHHo4mH424lnBHY9KVSHK94fpyMy9ry8V= hqiV1vTtMG0fms-pMqlJ6Pzo-szMpgzciOPiBYt12SghbAM$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4AzIGu5_fSSFHHo4mH424lnBHY9KVSHK94fpyMy9ry8V= hqiV1vTtMG0fms-pMqlJ6Pzo-szMpgzciOPiBYt159AGj-Y$=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. 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