LOCAL WEATHER CONDITIONS AT Franklin, Venango Regional Airport Temperature 62.6 F / 17 C Dew Point 57.2 F / 14 C Humidity 83% Wind Speed 12.7 Wind Direction SE 130 Degrees Visibility 10 Miles Sky Conditions overcast at 1400 feet Current Weather Barometer 30.09 Inches Issued At 05/04/2024 14:19 $$ |
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Area Forecast Discussion
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Day 1 Excessive Rainfall Outlook
FOUS30 KWBC 070051 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 750 PM EST Thu Dec 06 2018 Day 1 Valid 01Z Fri Dec 07 2018 - 12Z Fri Dec 07 2018 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER COASTAL SOUTHERN CALIFORNIA / LOS ANGELES/ SAN DIEGO... ...Southern California... In the 01Z update, we maintained the Slight Risk over far southern California while starting the process of trimming the northern portion of the Marginal and Slight risk areas. Satellite imagery shows the the mid/upper level circulation center about ready to come on shore with the coldest cloud tops mainly over land at this point. As of 01Z, observed rainfall rates were still getting up to 0.40 inches per hour, although the areal coverage of the heaviest rainfall was beginning to wane. The latest runs of the HRRR were suggesting that the rates will be back under a quarter of an inch per hour overnight. By that point, the focus of QPF will be making its way eastward This degree of rainfall could produce some rapid runoff situations, especially near burn scars. Bann Day 2 Valid 12Z Fri Dec 07 2018 - 12Z Sat Dec 08 2018 ...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHEAST TEXAS... ...Texas into the Lower Mississippi Valley... Ahead of a long wave trough tracking from southern CA to the Southern Plains during Day 2, a strengthening low level flow transports deep moisture from the western Gulf of Mexico northeast, increasing the threat for flooding/flash flooding across portions of TX into the Lower MS Valley. While the 12z GFS remains on the fast side of guidance, it is closer to the more consistent ECMWF, and some of its influence went into consideration for the Day 2 QPF and Excessive Rainfall Outlook (ERO). For the most part, there was little change in the overall ERO, with the Slight and Moderate Risk areas adjusted for trends in the guidance. Short wave energy ejected from the long wave trough moving toward north TX and OK interacts with deepening moisture from the western Gulf of Mexico, mainly during the 08/00z to 08/12z time frame. During that time, a 35 to 45 knot low level southerly flow transports 1.75/2.00 inch precipitable water air (which is between two and three standard deviations above the mean) along and over a frontal boundary extending from far South TX into far northeast TX. The moisture becomes entrained in developing frontogenetically forced bands of rain along the front, and there is a multi model signal for 3.00 to 6.00 inches of rain, mainly along and south of the frontal boundary. While moisture will be more than sufficient for heavy rainfall, instability still appears as though it will be lacking along and north of the front. Much of the 12z guidance showed instability remaining closer to the TX coast, with the rainfall maximum north of the best instability. The SREF probabilities of at least 250 J/KG of MUCAPE maximized along the middle TX coast, with very little or no instability just north of that. Model soundings along the expected axis of highest rainfall showed no instability, but a nearly saturated profile through at least 300 mb. The combination of synoptic scale lift and deep moisture could be enough to mitigate the lack of instability across East TX into southwest AR and northwest LA. Closer to the Texas coast, instability could be more of an influence, resulting in an enhanced flash flood threat. With this in mind the Moderate Risk was extended to the TX coast from Port Lavaca to Houston. The synoptic scale system is expected to be fairly progressive, which could mitigate a larger flash flood threat. Even though hourly rainfall rates may not support true flash flooding, The extent of the Slight Risk area was maintained. Hayes Day 3 Valid 12Z Sat Dec 08 2018 - 12Z Sun Dec 09 2018 ...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS THE GULF COAST AND PORTIONS OF THE SOUTHEAST... ...Gulf Coast into the Southeast... Moisture and instability ahead of a long wave trough crossing the Gulf Coast and Southeast will fuel low topped convection that produces heavy to excessive rainfall. There is still some model spread concerning the time of the mid level system, as well as its attendant surface system, with the 12z GFS remaining faster than the consensus, and the 12z NAM remaining a bit slower. Since the ECMWF has been more consistent with this system, the WPC QPF and the Day 3 Excessive Rainfall Outlook (ERO) was based on the two most recent ECMWF solutions. A weakening long wave trough tracks from from West TX into the western TN Valley during Day 3, and surface low pressure forming on a frontal boundary over the Upper TX Coast moves along the Gulf Coast. Ahead of the cold front associated with the surface low, a 50 knot low level southerly jet (which veers with time) transports 1.75/2.00 inch precipitable water (which is between two and three standard deviations above the mean) across the Gulf Coast into central MS/central AL and southwest GA. Model soundings (and SREF instability probabilities) indicate that the instability remains along the Gulf Coast, becoming elevated over southern portions of the Southeast states. The combination of instability and moisture is expected to feed low topped convection that crosses the abovementioned areas. Where the instability is deeper, there is a multi model signal for 2.50 to 3.50 inches of rainfall extending from southwest LA across southern MS/southern AL and the far western FL Panhandle. These amounts are close to the lower end of the three hour FFG values, especially over portions of the western FL Panhandle, where rainfall amounts over the past 14 days have been 400 percent of normal. Across these areas, A Slight Risk area was maintained. A Moderate Risk was briefly considered for the western FL Panhandle. were antecedent conditions are wet. However, the system should be progressive, which should mitigate an enhanced flash flood threat here. After collaborating with WFO TAE, the Moderate Risk was not assigned in the Day 3 ERO. Further north across northern portions the Gulf Coast into much of GA and SC, instability will be limited at best, as model soundings showed little in the way of instability above the cold air mass in place closer to the surface. In the right entrance of a 110 knot jet streak crossing the TN/OH Valleys, there should be sufficient synoptic scale lift to allow frontogenetically forced bands of moderate to heavy rain. There was a general consensus among the 12z model solutions to place 1.50/2.50 inches of rainfall in these areas, especially where any heavy rain bands train. At this point, it does not appear as though there will be hourly rainfall rates high enough to present a bonafide flash flood threat, but heavy rainfall could produce high streamflows here, so the Marginal Risk was maintained for Day 3. Hayes Day 1 threat area: http://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: http://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: http://www.wpc.ncep.noaa.gov/qpf/99epoints.txt $$
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