Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/07/18

Area Forecast Discussion
National Weather Service Boston/Norton MA
1047 PM EST Thu Dec 6 2018 .SYNOPSIS... Scattered snow showers cross the area tonight ahead of an approaching cold front. Otherwise, dry and cold weather persist across southern New England thru this weekend and into next week. High pressure in control allowing Arctic air to spill across the Northeast as the main storm track remains S of our region. Perhaps mild conditions and wet weather return for the following weekend. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 1020 PM Update... Band of light rain/snow showers has pushed into N CT out of the Litchfield hills and Berkshires. Temps across that area were mainly from 32 to 34 degrees at 03Z, so noting a few spots with either -SHRA or -SHSN, mainly across S CT, but can`t rule out a brief rain or snow shower as this precip moves across. As the precip shifts E through the pre dawn hours of Friday, will not see much in the way of accumulations as T/Td spreads across central and eastern areas were generally 10 degrees or greater, though could lower some with the light SW wind flow as the Arctic front crosses the region between 06Z and 12Z. Updated to bring conditions current and incorporate into the remainder of the overnight forecast. Previous Discussion... Sweeping Arctic cold front across the E Great Lakes region. Noting with the thermal discontinuity a brief burst of winds immediately behind the front collocated with steep lapse rates. Going with the latest HRRR with wind profiles to account for this. Gusts upwards of 30 mph possible. However, moisture and lift with the front are not extensive but could see scattered rain and snow showers ahead of and along the front. As winds shift from SW to NW towards daybreak Fri, column quickly dries back out and ends precip chances. Window for light wintry precip looks to range from around 00Z western MA/north central CT, until 09Z-12Z eastern MA/RI. Behind the front, a reinforcing shot of cold air will work in. Winds become gusty toward daybreak across the higher terrain of the interior, and along the coast. Overnight lows expected to be a couple of degrees below normal, mainly in the 20s. Some upper teens are possible in the higher terrain of far interior MA, and some lows in the low-mid 30s expected Cape/Islands and along the immediate shorelines of MA/RI. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Friday... Will be a dry but cold day, as cold air advection continues and surface high pressure builds eastward towards our area. It will be a blustery day, as W-NW winds increase. Wind gusts should top out at 25-30 mph, though a few higher terrain locales may see a few higher gusts. Sunny/mostly sunny skies forecast, with a few diurnal stratocumulus clouds. Highs expected to be 5 to 10 degrees below normal for early December, mainly in the 30s. Anticipate some upper 20s across the far interior higher terrain, and some highs around 40 mainly on the Cape and Islands. Friday Night... Dry conditions continue, and thanks to cold air advection from Friday, potential for chilly overnight lows in place. Short wave energy passing over the area could bring some passing clouds. However, overall expecting mainly clear skies and diminishing winds, which will allow for good radiational cooling. Lows in the teens expected for much of the area. Portions of the far interior will probably see mins in the single digits, especially where there is a snow pack in place. && .LONG TERM /SATURDAY THROUGH THURSDAY/... */ Highlights... - Cold, dry conditions into mid-December - Watch for ocean-effect snows along coastal E MA at times - Warmer, wetter weather potentially returning around mid-December */ Overview... This pattern is crazy. +ENSO / El Nino Winter resemblance, dominant H5 N Pacific low contributing to +EPO / +WPO signals. Subsequent H5 ridging into N America, accompanying +H85 temperature anomaly into Canada. From noted H85 and H2 westerly perturbations from evolving +ENSO / El Nino, echoing upward through the stratosphere, there is a resultant cross-polar flow downsheared E of the aforementioned ridge that evolves across Eastern N America into the N Atlantic. While NE CONUS slightly colder than average conditions prevail, the H3 sub- tropical Pacific jet and storm track is pushed S, yielding overall dry conditions through mid-December, notably with -NAO / -AO trends that indicate downstream N Atlantic progressive storm pattern while Arctic air is released S equatorward across the N Hemisphere. Tele- connections noted above netting a seasonable 2m temperature balance through December as negative 2m temperature anomalies prevail into mid-December, with mild Pacific warmth finally edging in around mid- December continuing potentially through the end of the month as the aforementioned cross-polar flow shifts E, a dipole of stratospheric vortices rotating round the N Hemisphere, the MJO sliding from a phase 2 towards 4 adding to warm westerly perturbations. A potential return of the storm track N and wetter conditions by mid-December. */ Discussion... A 10-day dry stretch ongoing and forecast which we haven`t seen in meteorological winter since 2016, prior to that in 2010. Initially very cold, Arctic air for the weekend associated with high pressure that`ll keep the storm track well S off the SE CONUS per consensus of forecast model guidance. However, with deepening storms to our S comes the isallobaric response. -AO trend, Arctic air unlocked, on into Thursday morning we could see some of the coldest air of the season beneath -12 to -18C H85 Arctic airmass. Blustery N winds at times which will make it feel colder with respect to wind chills, will be watching for any ocean-effect snows across E MA that`ll occur given a colder airmass over warmer waters, watching the depth of moisture parent with any instability. As the associated high pressure shifts E into the following weekend, we potentially could see a significant warm-up and return of wetter conditions. && .AVIATION /04Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/...High confidence. 03Z update... Overnight... Mainly VFR, with CIGS lowering to BKN040-060. May see brief lowering of CIGS to MVFR with any scattered rain or snow. Isolated IFR conditions possible across E slopes of the Berkshires. Conditions should improve from W-E after 08Z, but may linger across E Mass/RI through 12Z Fri. Friday into Friday night... VFR conditions expected. W-NW wind gusting to 20-25 kt, possibly up to 30 kt across the higher terrain and along the coast. Winds tapering into the overnight hours. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Saturday through Tuesday/... Saturday through Saturday Night: VFR. Breezy. Sunday: VFR. Sunday Night through Monday Night: VFR. Breezy. Tuesday: VFR. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/...High confidence. Overnight... Small Craft Advisory headlines in place. SW winds will increase this evening, expecting gusts up to 25-30 kt, highest across the southern waters with seas increasing to 5-7 ft. Scattered rain and/or snow showers move across with visibility locally reduced as the precip moves across, but should improve from W-E after 09Z. Friday... Winds shift to NW Fri morning with continued gusts up to 25-30 kt, with winds diminishing during the afternoon. Seas on the outer waters 5-7 ft. SCA headlines continue for the coastal waters, except for Narragansett Bay. Friday Night... NW wind gusts around 25 kts early, otherwise winds gradually diminishing. Seas also gradually subsiding. SCA headlines continue for the outer coastal waters. Outlook /Saturday through Tuesday/... Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Sunday through Sunday Night: Winds less than 25 kt. Monday: Winds less than 25 kt. Seas locally approaching 5 ft. Monday Night through Tuesday: Winds less than 25 kt. Seas up to 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 4 PM EST Friday for ANZ232>234. Small Craft Advisory from 3 AM to 4 PM EST Friday for ANZ230. Small Craft Advisory until 6 PM EST Friday for ANZ231-235-237- 251. Small Craft Advisory until 7 AM EST Friday for ANZ236. Small Craft Advisory until 5 AM EST Saturday for ANZ250-254- 255. Small Craft Advisory until 1 AM EST Saturday for ANZ256. && $$ SYNOPSIS...Sipprell/NMB NEAR TERM...Sipprell/EVT/NMB SHORT TERM...NMB LONG TERM...Sipprell AVIATION...Sipprell/NMB MARINE...Sipprell/NMB
Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
742 PM EST Thu Dec 6 2018 .UPDATE... Zonal flow aloft starting to bring upper moisture and cirrus from Mexico across the Gulf. Locally, moisture and temps moderating late this afternoon and early evening as seen in 00Z sounding with PWATs up to a half inch. Surface high pressure over the Deep South keeping easterly low level flow over the FL Peninsula under inversion at 4k ft. Latest grids and forecasts on track with cool night around 5 degrees below seasonal averages. && .AVIATION... VFR conditions overnight with light winds and SCT cirrus. && .MARINE... 3-4 mb gradient over the E Gulf this evening with slight evening easterly surge but conditions to remain below headlines. Latest buoy obs showing winds around 2 ft and winds 5-10 kts nearshore and 10-15 kts offshore. && .Prev Discussion... /issued 221 PM EST Thu Dec 6 2018/ ..Updated to include sea fog potential and severe weather threat discussions for Saturday Night and Sunday... SYNOPSIS... 19Z water vapor and H4 RAP analysis show a mid/upper level zonal flow pattern in place over the northern Gulf/Deep south states. Stacked WV imagery shows very dry air in the middle levels of the atmosphere underneath a slight influx of higher level moisture (noted by some passing cirrus over the northern parts of the state). This satellite analysis is confirmed by the 12Z KTBW RAOB, which indicates this drier layer below roughly 500mb, and a lower dewpoint depression further up into the troposphere. Even with this influx of upper moisture, the column itself as a whole is extremely dry. The measure PW value from the sounding was only 0.23", which equates to roughly a 5th percentile of values for early December. In fact, for the date itself, its a new record low PW, with the previous record low value being 0.35"...although granted...the old record was a rather high value compared to other nearby dates. Never the less, its dry. In the lower levels we find 1030mb high pressure centered over AL/GA/Carolinas, which will hold in place through tonight. The flow around this ridge to our north keeps a general NE/E flow pattern in place. The proximity of the high center and dry lower levels allowed us to start today with some rather chilly readings (at least for Florida). Many spots along and north of the I-4 corridor dropped down into the 30s, with even a few normally colder locations briefing seeing upper 20s around sunrise. South of I-4, widespread 40s were seen, with localized cold spots in the upper 30s. We will now begin a gradual warming trend into the upcoming weekend, which will prevent any additional threat of freezing temperatures. SHORT TERM (Rest of Today through Friday)... No significant weather concerns are anticipated through the remainder of the work week. High pressure to our north this afternoon will hold in place through tonight before gradually shifting eastward over the Atlantic during Friday/Friday night. Last night was the coldest night of the week, and we will now begin a slow but noticeable warm-up that will continue into the upcoming weekend. The rest of today will see mostly sunny skies and light easterly winds, with high temperatures reaching the lower/mid 60s north of the I-4 corridor and upper 60s to lower 70s further to the south. We are still looking for a "chilly" Florida type night, but not nearly as cold as last night. Most locations can likely add a good 5-8 degrees to their low temps from last night, which will keep all area above freezing, even across the northern Nature Coast. Low temps by sunrise Friday should reach the upper 30s to middle 40s north of I-4, and generally fall in the upper 40s to lower 50s further to the south. Based on the current temp forecast. A few normally colder locations north of Brooksville could see a brief period of frost around sunrise Friday, but this would be limited to high localized and sheltered locations. A very pleasant day looks to be in store for Friday across the region under surface high pressure and continued zonal flow aloft. Embedded within the zonal flow along the northern Gulf coast look to be a series of very subtle shortwave impulses. While these disturbances have little impact on the lower atmosphere, it is likely that they will support at least passing high level cirrus, if not fully filtered sunshine over the northern half of the peninsula. Otherwise, look for mostly sunny skies for the southern half of the region. High temperatures continue their climb on Friday, reaching the upper 60s to lower 70s north of I-4, and generally the middle 70s further to the south. LONG TERM (Saturday through next Thursday)... The synoptic pattern across the central and eastern parts of the CONUS will begin to change rapidly as we head through the first half of the upcoming weekend. Our next weather maker will begin to take shape as longwave troughing ejects quickly eastward over the southern Plains and lower MS Valley. For us, this means that if you would like to enjoy some outdoor activities this weekend, the "better" weather day is almost certainly going to be Saturday, as rain chances stay near 0%. For those with marine plans, Saturday will be much better in terms of rain chances, however, winds will already by ramping up from the southeast and south, making boating conditions a bit on the rougher side. As is often the case, the height falls to our west associated with the approaching trough will help boost downstream heights over us for the day on Saturday. The enhanced ridging aloft will enhances the temperature potential, and the current forecast has all locations in the region reaching at least the lower 70s, with middle and upper 70s common south of I-4. Not out of the question that spots around Fort Myers and away from the immediate coast will make a run at 80 Saturday afternoon. Saturday night into Sunday the trough and an associated surface reflection/low move quickly eastward along the northern Gulf coast. A cold front will trail south from this low through the central Gulf and also move quickly eastward toward our region by Sunday morning. Saturday night looks rather warm around these parts are steady southerly flow brings ever increasing tropical air northward across the peninsula. Much of the overnight (especially Saturday evening) looks to remain dry, as it will not be until the late night hours that rain chances begin to increase from the west ahead of the cold front. The best chances for rain/storms before sunrise Sunday should exist over the coastal waters and Nature Coast, and then spread east and southward fairly quickly Sunday morning/early afternoon. As with many our winter systems, an all day rain is not expected, but rather a couple of hours of wet weather associated with a band of rain/storms along the front. The upper level support and surface convergence look good enough with this system to expect a wetting rainfall for most location, although highest rainfall amount potential will exist north of I-4 in closer proximity to the best height falls/QG forcing. The front will be a steady mover and exit stage right during the later afternoon/evening hours of Sunday. Showers and storms will exit with the front, followed by the arrival of our next shot of cooler and drier air for the early part of next week. This airmass will arrive on elevated northwesterly winds that will bring rough conditions to the eastern Gulf of Mexico, and likely an increased risk of rip currents along our beaches through at least Monday. So what about the threat for severe storms Sunday? As is almost always the case this time of year along the FL west coast, we will be dealing with a high shear / low CAPE scenario with this passing front. Although the shear is mainly unidirectional, it is quite strong no matter what guidance solution one examines. I tend to lean away from the 70+ low level jet values advertised by the 12Z GFS over the Nature Coast, as these seem influenced by convective processes/feedback within the model. However, low level jet peak values near 50kts in the GFS-FV3 and NAM and resulting deep layer bulk shear values of 45-55kts are certainly decent as well, and certainly supportive of organized convection. These values suggest a damaging wind threat with some of the storms Sunday...if...if...they are surface based. This is the big question. The best potential for adequate surface based instability to bring winds to the surface lies mainly south of the strongest winds aloft, but its a close call. We will need to see the impact of the latest cold snap and offshore winds on the shelf water temps, especially off the Nature Coast. The cooler these waters get, the less likely we will see substantial surface based instability into these zones. Simply stated, there is a threat for some stronger storms Sunday along this front, especially from the I-4 corridor northward, and we will have to monitor instability trends as we get closer to the event to determine if its a substantial threat, or something that looks good in NWP and on radar, but does not materialize at ground level where the impact matter to us. As it looks now, the period of Monday through next Thursday look dry, but cool for our part of the state. A little early to get into detail of whether there will be another threat for sub-freezing temperatures, as much will depend on the exact track of the high center into the southeastern states during the early/middle portion of the week. If a threat for freezing temps does develop, it would most likely occur Tuesday and/or Wednesday night. The better potential would also exist over the Nature Coast counties in closer proximity to the likely ridge center location and in better conditions to support boundary layer decoupling/enhanced radiation cooling. After midweek, anther gradual warming trend should commence. AVIATION (06/16Z through 07/18Z)... VFR conditions will prevail through the TAF period. NE/E winds between 6-9kts settle down to 5kts or less overnight into early Friday morning. MARINE... High pressure remains to our north through tonight before shifting eastward over the Atlantic on Friday. Northeast to easterly winds continue through Friday before shifting southeast and then south and increasing on Saturday ahead of the next approaching cold front. This front will cross the forecast waters during Sunday with our next chance of rain and storms. Mariners can expect a period of cautionary to advisory level winds and seas both preceding and in the wake of this frontal passage. High dewpoint air surging northward Saturday night into Sunday morning may set the stage for a period of sea-fog potential over the nearshore waters...mainly south of Tarpon Springs. These sea-fog events can be impacted by very subtle changes in the forecast, so for now will simply add fog wording in the forecast. More details will emerge during the next 24-48 hours if a fog/visibility threat during the second half of the weekend appears to continue. Any sea-fog that does develop will end quickly later Sunday afternoon/eve as the cold front passes by. FIRE WEATHER... High pressure hold in control of the region through Friday, providing a NE/E wind flow across the Florida peninsula. Temperatures will see a gradual warming trend into the upcoming weekend, however, a slow increase in low level moisture will prevent any widespread regions of critically low relative humidity through Friday. By the weekend, all areas will see relative humidity well above critical levels. The next chance of rain/storms will arrive Sunday with a cold front. Much of the area is likely to see a wetting rainfall with this frontal passage, followed by drier and cooler air, under a northwesterly to northerly wind pattern for the early portion of next week. Fog Potential...No significant fog or visibility issues are expected through Friday. && .Preliminary Point Temps/PoPs... TPA 49 74 58 78 / 0 0 0 0 FMY 53 77 60 80 / 0 0 0 0 GIF 48 75 57 79 / 0 0 0 0 SRQ 53 74 60 77 / 0 0 0 0 BKV 44 74 55 79 / 0 0 0 0 SPG 53 74 60 78 / 0 0 0 0 && .TBW WATCHES/WARNINGS/ADVISORIES... FL...None. Gulf waters...None. && $$ UPDATE/AVIATION/MARINE...25/Davis UPPER AIR...19/Hurt DECISION SUPPORT...69/Close