Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/30/20

Area Forecast Discussion
National Weather Service Jacksonville FL
903 PM EST Sun Nov 29 2020 ...ISOLATED SEVERE THUNDERSTORM THREAT OVERNIGHT TONIGHT... .UPDATE... Water vapor imagery shows a strong mid/upper[er level trough to our west with good divergence at 250 mb headed our way. Mid to high clouds are spreading downstream over our region at this time. The warm front appears to have lifted north to near the FL/GA state line, with the cold front located over AL from a 1007 mb sfc low, then south-southwest into the Gulf of Mexico. Sfc based CAPE continues to be very limited so far in our area is below 200 J/kg. JAX sounding at 00z showed a stable airmass but fairly strong veering and a 0-6 km bulk shear of 54 kt. Based on latest HRRR model guidance, timing of heavier showers and potential storms, along and ahead of the cold front, looks to be about 11pm- midnight over our western GA zones and then pushing east about 25-30 mph through the night. This places the front and precip along the east coast about 7AM-9AM Monday. As far as the isolated severe t-storm threat, there is a narrow corridor of instability right along and just ahead of the front. Here is where a damaging wind gust or a brief spin-up of a tornado will be possible, with the main threat area from inland southeast GA southward into the Suwannee Valley area. Further east, instabilty will be weaker but nonetheless, strong wind gusts in convection cannot be ruled out and wind gusts upwards of 40-60 mph will be possible. Clearing skies and gusty westerly winds expected by mid morning on Monday as the cold front pushes further offshore. Given the quick moving front, rainfall amounts will generally be less two-thirds of an inch. Main updates this evening were to delay precip a bit for this evening and lower t-storm probabilities for the next 3-4 hours given the weak instability thus far. && .PREV DISCUSSION [650 PM EST]... .NEAR TERM [Tonight through Monday]... Currently, a warm front is situated roughly along the I-10 corridor. As the front has lifted northward this afternoon, the cirrus shield has slowly eroded allowing weak destabilization across NE Florida, evident by a patchy cumulus field. These updrafts will battle with dry air aloft and strong mid-level (3-6 km) shear, which is likely to be more destructive than beneficial at this point. That said, outside of an isolated shower, conditions should remain quiet south of the front through the evening. North of the warm front, overrunning showers and overcast conditions will continue for the next several hours. The warm front will continue to lift across GA through the evening hours. A deepening surface low near the MS/AL coast will deepen and race northeastward tonight as the associated upper low is absorbed by an upstream trough. As it does, the lower tropospheric wind fields will increase resulting is very strong deep shear and sufficient helicity parameters across the region this evening. The cold front trailing behind the surface low will press across the region late this evening through pre-dawn hours Monday. A line of strong and isolated severe thunderstorms will be possible for across the inland SE GA zones and Suwannee River Valley areas late tonight as an axis of instability develops amid strong wind shear ahead of the cold front; risk for isolated tornadoes will be highest in these locations. The line of showers and thunderstorms will continue eastward toward the Atlantic coast but will start to fracture as instability begins to decrease early Monday morning. Though the severe risk will start to wane with weakening instability, an isolated damaging straight-line wind threat will exist, especially with an localized bowing segments on the line. Expect the line to clear out of SE GA shortly after Sunrise Monday and NE FL by noon or earlier, leaving breezy west winds and clearing skies in it`s wake. Temps will remain in the low to mid 60s overnight ahead of the approaching cold front/line of thunderstorms. For SE GA the warmest temperatures on Monday will occur in the morning, as cold air funnels in behind the front. By 4 PM Monday, temps will fall to the low to mid 50s across inland SE GA and the Suwannee River Valley and to the upper 50s and low 60s along the coast and north-central FL. Temps will continue to fall Monday night, bottom out in the mid-30s for across inland SE Georgia and Suwannee valley and to the upper 30s and low 40s along the coast and north-central Florida. .SHORT TERM [Tuesday through Wednesday]... Much colder with inland freeze potential as surface high pressure builds eastward across the Gulf Coast states. Below normal highs will only range in the 50s to upper 40s for parts of inland SE GA Tue, with some moderation of temps into Wed as upper level WSW flow develops ahead of the next frontal system. The main weather impact this periods will be an inland freeze Tue night for SE GA and the Suwannee River Valley of NE FL where lows in the upper 20s are expected. For coastal SE GA generally west of the I-95 corridor a light freeze is expected extending southward across inland Nassau and Duval counties, western Clay-Putnam and Marion counties. There could be some patchy frost, but at this time airmass looks too dry to support significant frost formation. Another light inland freeze is expected across parts of inland SE GA Wed night but moisture and temps will increase from the east as onshore flow develops as the surface high builds NNE of the local area. Wed night may actually be the better night for some patchy frost as lows fall into the mid 30s inland. .LONG TERM [Wednesday Through Sunday]... Temperatures further moderate back toward near climo values Thu as high pressure shifts farther offshore of the mid-Atlantic coast in advance of a stalling frontal system. This boundary will gradually settle southward across the SE region Fri into Sat while beginning to stall as stronger upper level forcing lifts NE. Elevated moisture and forcing near the meandering front return rain chances to the local area Fri. A stronger upper level low passes quickly across the deep south on Saturday, bringing the potential of thunderstorm activity. Ultimately depends on where the stalling front lingers in terms of rainfall amounts and t`storm outlook and confidence in the details remains too low at this time. A much drier and cooler airmass returns Sunday under drier post- frontal deep layer WNW flow with surface high pressure building eastward from the TX Gulf Coast early next week. .AVIATION... [Through 00Z Tuesday] A warm front continues to slowly push northward over northeast FL this evening. Brief period of cig restrictions looks possible from SGJ northward this evening but overall chances will diminish by about 04Z-05Z as the front lifts northward. Later on tonight cloud cover will increase and southerly winds increase as a pre- frontal line of gusty showers and isolated tstorms approaches as a cold front moves into the area. Showers and VCTS are indicated in the terminals for now after 08z through about 12Z-14z. In addition, some LLWS is noted in the terminals from JAX metro area northward as low level jet increases to 40-45 kt at about 1500-2000 ft. Breezy south- southwest winds will increase into the 10-13 knots before sunrise ahead of the front. Showers and the front will push offshore 13Z-15z with just lingering light showers and low clouds through mid to late morning or so. Gusty post-frontal westerly winds expected and developing VFR. Some guidance suggests some wrap around clouds late Monday aftn but too low confidence to include any cig restrictions. .FIRE WEATHER... Potential for elevated fire danger Tue due to breezy WNW winds combined with low humidity in at least the lower 30s. && .PRELIMINARY POINT TEMPS/POPS... AMG 55 61 32 49 27 / 80 30 0 0 0 SSI 61 69 37 52 34 / 60 60 0 0 0 JAX 62 69 36 53 32 / 60 60 0 0 0 SGJ 65 73 39 55 38 / 40 70 0 0 0 GNV 62 69 35 53 29 / 70 60 0 0 0 OCF 65 71 36 55 31 / 70 70 0 0 0 && .JAX WATCHES/WARNINGS/ADVISORIES... FL...None. GA...None. AM...Small Craft Advisory until 11 PM EST Tuesday for Waters from Altamaha Sound GA to Fernandina Beach FL from 20 to 60 NM- Waters from Fernandina Beach to St. Augustine FL from 20 to 60 NM-Waters from St. Augustine to Flagler Beach FL from 20 to 60 NM. Small Craft Advisory from 3 AM Monday to 11 AM EST Tuesday for Coastal waters from Altamaha Sound to Fernandina Beach FL out 20 NM-Coastal waters from Fernandina Beach to St. Augustine FL out 20 NM-Coastal waters from St. Augustine to Flagler Beach FL out 20 NM. &&
Area Forecast Discussion
National Weather Service Nashville TN
738 PM CST Sun Nov 29 2020 .UPDATE... FOR EVENING DISCUSSION. && .DISCUSSION... A deepening surface low is currently moving northeastward across the state of Alabama, with an inverted trough extending northward from the low and bisecting Middle Tennessee. The 00Z sounding from OHX shows a nearly saturated column extending from near the surface to almost 500 mb. While there is no instability to speak of, precipitable water is a robust 1.10" and a strong southwesterly 120-knot jet is centered around 300 mb. The aforementioned low will continue along its present track into the Appalachians later tonight, and this will result in a tightening pressure gradient on the back side of the low and also plenty of wrap-around moisture to go along with the cold advection. Also tomorrow, an unusually strong low height center will descend from the upper midwest and keep our upper-level pattern highly amplified. The latest HRRR shows most of tonight`s precipitation exiting the mid state by 12Z, after which light echoes resulting from the wrap-around moisture and closed upper low will begin to fill in across Middle Tennessee. At any rate, the current forecast appears to be in good shape. The hourly grids are holding up reasonably well and no changes are needed for now. && .AVIATION... 00Z TAF DISCUSSION. Rain will impact the terminals overnight with heavier activity expected by 03z as surface low pressure lift NE closer to the area. There should be a break between this activity and the wrap around activity that will begin to impact CKV by 12z. Temperatures will fall through the morning and afternoon and rain will transition to a rain/snow mix before ending as all snow. CSV will experience the heaviest snow after 21z which could reduce vis to less than 1 sm. Northwest winds will increase overnight to 10-15 kts with gusts up to 25 kts at times. && .OHX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 3 PM Monday to 6 AM CST Tuesday for Cumberland-Fentress-Overton-Pickett-Putnam-Van Buren-White. && $$ DISCUSSION......08 AVIATION........Reagan