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From | To | Subject | Date/Time | |||
COD Weather Processor | wx-storm | HVYRAIN: Excessive Rainfall Discussion |
July 28, 2019 8:07 AM * |
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This is a multi-part message in MIME format... ------------=_1564301277-118394-1340 Content-Type: text/plain FOUS30 KWBC 280807 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 407 AM EDT Sun Jul 28 2019 Day 1 Valid 01Z Sun Jul 28 2019 - 12Z Sun Jul 28 2019 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE NORTHERN PLAINS AS WELL AS PARTS OF THE CENTRAL AND SOUTHERN ROCKIES... ...Northern Plains... The upper ridge over the northern-central Rockies has flattened a bit during the day in response to a shortwave trough skirting the northwest U.S./southwest Canadian border along with a convectively-aided vort lobe that has yet to drop into the high plains during the evening. Strengthening south to southeast low-level flow ahead of the aforementioned vort and associated surface low will help draw a more moist and unstable airmass farther northwest and into eastern WY and southeast MT. MUCAPES should have already peaked in the 1500-2500 j/kg range at the time of peak daytime heating hours this afternoon, and should gradually decrease to values at or below 1000 j/kg later tonight. Precipitable Water values were forecast to climb to around 1.25" across the high plains and to 1.50+ farther east...and the 28/00Z sounding tended to be pretty close to those. That amount of moisture is modestly anomalous for late July (around 2 standard deviations above normal). The Slight Risk was expanded a bit based on late afternoon/early evening radar trends...but still delineates areas of lower FFG -- i.e. 1" or less within one hour and 1-1.5" within 3 hours. The latest HREF and experimental HREF both depict the highest exceedance probabilities across a portion of southwest SD through 28/03Z. ...Central and Southern Rockies/Intermountain West... Some of the convection over parts of the Intermountain West as well as the Central and Southern Rockies have produced heavy downpours...especially the storms peeling off the mountains which interact with outflow from earlier convection. Rainfall rates of 1.5 to 2 inches per hour have been depicted on area 88Ds...although the dual-pol HCA has also depicted decent coverage of hail. In general, though, low-level east to southeast flow will continue to transport 1.00-1.25 inch PWs across the front range of the CO/NM mountains. Farther west, in the Great Basin, the convection has been weakening with the loss of solar heating. The Slight Risk area was trimmed considerably from the Great Basin area and confined to a narrow ribbon along and east of the Front Range. Bann Day 2 Valid 12Z Mon Jul 29 2019 - 12Z Tue Jul 30 2019 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHERN ROCKIES INTO THE SOUTHWEST...AS WELL AS THE LOWER MISSISSIPPI VALLEY INTO THE OHIO VALLEY... ...Southern Rockies into the Southwest... As the mid level ridge reasserts itself over the Southwest states, the monsoonal flow becomes reestablished over the Southwest and Southern Rockies during Day 2. While the best thrust of moisture is expected across southern AZ (where precipitable water values rebound to near 1.75 inches before 30/12z), the best instability is expected across the Southern Rockies into the Sangre de Cristo Mountains. An axis of 500/1000 J/KG of MLCAPE is expected to develop from the Front Range of the Rockies in CO into northern and southwest NM, peaking near 30/00z. The developing storms will tap 1.00 inch precipitable water air on a low level southeast flow to produce local 1.00 inch rainfall amounts over the higher terrain, where the storms will be almost stationary against the upslope flow. Once maximum heating occurs, the storms will begin to move slowly west northwest with the weak mid level flow, retaining the potential to produce hourly rainfall rates between 0.50/1.00 inches away from the terrain. Three hour flash flood guidance values are as low as 1.50 inches in these areas, so a low end flash flood threat is expected. Based on the above, a Marginal risk was placed over the higher terrain and adjacent locations. Further west across southeast AZ, the moisture plume from northern Mexico possesses more moisture than CO/NM, but instability could end up being the limiting factor for a more organized flash flood threat. Scattered storms could produce local 1.00 inch rainfall amounts over the higher terrain before moving out into lower terrain, but the general lack of forcing would suggest that the storms should be short lived. Slow cell motions under the ridge position could allow for cell mergers and short training. Based on the above, the Marginal Risk was extended across southeast AZ for Day 2. ...Lower Mississippi Valley into the Ohio Valley... Moisture and instability extending ahead of a slowing cold front are expected to feed convection that could produce locally heavy rainfall from the Lower MS Valley into the OH Valley during Day 2. The best moisture feed ahead of the front is expected across MO into AR/OK, mainly between 29/18z and 30/06z. Model soundings showed an axis of 1500/2500 J/KG of MLCAPE in line with the deepest moisture, and developing storms are expected to drop southeast with the mid level flow. Slow storm motions along the front as it becomes quasi stationary in the 1.75/2.00 inch precipitable water air pooled near the front could allow hourly rainfall rates to approach 2.00 inches, mainly over AR around 30/00z. After that, there is a model signal that a cold pool could form with storms over AR, resulting in the storms dropping south into northern LA as they weaken. Three hour flash flood guidance values are generally above 2.50 inches from MO into northeast OK, and above 3.50 inches over much of the Lower MS Valley. Slow storm motions (especially early, before any outflow driven storms form) could produce rainfall amounts near the lower end of the spectrum, especially over portions of AR and southern MO. Based on the above, a Marginal Risk was placed over much of the Lower and a portion of the Mid MS Valley for Day 2. Further northeast along the front, the axis of moisture and instability extends into the OH Valley, where storms along the front across slow as the mid level flow becomes more parallel to it. The 00z NAM CONUS Nest indicated the potential for hourly rainfall rates to approach 1.50 inches over IN/OH and northern KY. Three hour flash flood guidance values here are generally above 2.50 inches, but short term training in the higher moisture air environment could allow storm totals to reach close to these values. Based on this, the Marginal Risk was extended into the Ohio Valley for Day 2. Hayes Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.t... Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.t... Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.t... $$ ------------=_1564301277-118394-1340 Content-Type: text/plain; charset="US-ASCII" Content-Disposition: inline Content-Transfer-Encoding: 7BIT = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. ------------=_1564301277-118394-1340-- --- SBBSecho 3.07-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) |
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