jeffl
04-24-2005, 07:05 PM
Once again another complicated forecast for SE TX.
Strong upper trough now centered over the Great Basin will eject into the New Mexico high plains early Monday with rapidly developing surface low pressure over SE CO moving to the central Red River valley late Monday.
Air mass is currently very dry with dewpoints in the 30's and PWS near .25in. Forecast models suggest rapid air mass modification tonight into Monday with low to upper 60 degree dewpoints streaming N from the Gulf. Given that E and NE winds remain across much of the Gulf and 60 degree dewpoints are confined to well south of Brownsville leaves question as to if moisture return will be as strong as forecast. We will not know until tomorrow with the morning RAOB's (soundings).
Regardless of moisture, potent surface low NW of Fort Worth during the afternoon hours of Monday will send the dryline into central TX. CAPE values are strongly tied to moisture return but should be into the 1500-2500 J/kg range by mid afternoon. LI's fall to -6 to -8 with good amounts of low level shear. In fact the ETA is going "bonkers" with the shear with 200-300 m^2/s^2 of helicity within the lowest 3 km and 0-1 km values of 150-250. Low level flow will remained backed (from the E and ESE) over E TX due to surface low location and warm frontal boundary favoring supercells and a tornado threat.
With enough clearing and "moisture return" severe thunderstorms will erupt along the dryline by late afternoon along or just E of I-35. Initial mode should be isolated to scattered supercells with large hail and tornadoes the primary threat. Threat will gradually transition into line segments with BOWS and LEWPS and/or an MCS with damaging winds.
Once again quality of low level moisture return is critical in the forecast of severe weather and any rainfall for that matter. Current dry spell would push forecaster confidence toward a more non-event (Friday) due to persistence and a developing feedback relationship with the coupled ground/atmosphere moisture profiles.
However given the high instability and very favorable shear profiles one cannot discount a future event based on the experiences of the last 3-5 weeks. One of many dilemmas with weather forecasting.
Jeff Lindner
Strong upper trough now centered over the Great Basin will eject into the New Mexico high plains early Monday with rapidly developing surface low pressure over SE CO moving to the central Red River valley late Monday.
Air mass is currently very dry with dewpoints in the 30's and PWS near .25in. Forecast models suggest rapid air mass modification tonight into Monday with low to upper 60 degree dewpoints streaming N from the Gulf. Given that E and NE winds remain across much of the Gulf and 60 degree dewpoints are confined to well south of Brownsville leaves question as to if moisture return will be as strong as forecast. We will not know until tomorrow with the morning RAOB's (soundings).
Regardless of moisture, potent surface low NW of Fort Worth during the afternoon hours of Monday will send the dryline into central TX. CAPE values are strongly tied to moisture return but should be into the 1500-2500 J/kg range by mid afternoon. LI's fall to -6 to -8 with good amounts of low level shear. In fact the ETA is going "bonkers" with the shear with 200-300 m^2/s^2 of helicity within the lowest 3 km and 0-1 km values of 150-250. Low level flow will remained backed (from the E and ESE) over E TX due to surface low location and warm frontal boundary favoring supercells and a tornado threat.
With enough clearing and "moisture return" severe thunderstorms will erupt along the dryline by late afternoon along or just E of I-35. Initial mode should be isolated to scattered supercells with large hail and tornadoes the primary threat. Threat will gradually transition into line segments with BOWS and LEWPS and/or an MCS with damaging winds.
Once again quality of low level moisture return is critical in the forecast of severe weather and any rainfall for that matter. Current dry spell would push forecaster confidence toward a more non-event (Friday) due to persistence and a developing feedback relationship with the coupled ground/atmosphere moisture profiles.
However given the high instability and very favorable shear profiles one cannot discount a future event based on the experiences of the last 3-5 weeks. One of many dilemmas with weather forecasting.
Jeff Lindner