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Nick F

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Posts posted by Nick F

    Convective/Storm Discussion Thread - 1st August onwards

    in Storms & Severe Weather

    Posted

    Storm & Convective Forecast

    convmap_250817_1.thumb.png.f062a70ad3cd634849d67678080c8bd0.png

    Issued 2017-08-25 08:06:27
    Valid: Friday 25 Aug 6am to Saturday 26 Aug 6am

    Day 1 Convective /Storm Forecast

    Synopsis

    An upper and collocated surface low to the west of Scotland will gradually drift east across Scotland during the forecast period. Heavy showers and thunderstorms are likely across Scotland and N. Ireland, then perhaps over N England overnight.

    ... SCOTLAND, N of Rep. of IRELAND and N. IRELAND ...

    Upper low close to NW Britain will create steep lapse rates and create large scale ascent which will support scattered heavy showers and thunderstorms away from frontal cloud and rain areas. Weak vertical shear will mean severe weather is unlikely, though any heavy showers/storms will be slow-moving leading to a risk of localised flooding where they pass. Showers/storms may also produce small hail and gusty winds. Light winds aloft and surface convergence may produce funnel clouds or even a brief/weak tornado with stronger updrafts. Showers and isolated storms may continue overnight as they drift east across Scotland with the upper/surface low, lightning activity may increase along east coast as cells move out over N Sea with warm SSTs (sea surface temps) creating bouyancy.

    ... N ENGLAND ...

    As upper low crosses Scotland tonight, pool of steep lapse rates generated over relatively warm Irish Sea SSTs will support heavy showers and a few thunderstorms pushing inland and east across N England overnight. with a risk of localised flooding from stronger cells. Lightning activity may increase as cells move out over the N Sea and over warm SSTs.

    Issued by: Nick Finnis

    Hurricane Harvey

    in Hurricanes, Cyclones and Extreme weather worldwide

    Posted

    Upto 35 inches of rainfall and 6-12ft storm surge :shok::shok: http://www.nhc.noaa.gov/text/refresh/MIATCPAT4+shtml/242045.shtml

    Quote 
    
HAZARDS AFFECTING LAND
----------------------
RAINFALL:  Harvey is expected to produce total rain accumulations
of 15 to 25 inches and isolated maximum amounts of 35 inches over
the middle and upper Texas coast through next Wednesday. During the
same time period Harvey is expected to produce total rain
accumulations of 7 to 15 inches in far south Texas and the Texas
Hill Country over through central and southwest Louisiana, with
accumulations of up to 7 inches extending into other parts of Texas
and the lower Mississippi Valley. Rainfall from Harvey may cause
devastating and life-threatening flooding.
    Quote 
    
STORM SURGE:  The combination of a dangerous storm surge and the
tide will cause normally dry areas near the coast to be flooded by
rising waters moving inland from the shoreline.  The water is
expected to reach the following heights above ground if the peak
surge occurs at the time of high tide...

N Entrance Padre Island Natl Seashore to Sargent...6 to 12 ft

     

    Hurricane Harvey

    in Hurricanes, Cyclones and Extreme weather worldwide

    Posted · Edited by Nick F

    30 minutes ago, SNOW_JOKE said:

    Windyty has Harvey as barely making it inland past Corpus Christi, bouncing back off the coast into the Gulf, then re intensifying to make landfall again around Baton Rogue before dissipating.

    little steering flow to keep it moving inland, even if it is currently moving NW at 10-15mph overland it will have little impetus to keep that track, a look at the 50 EPS perturbations suggests many keeping Harvey hugging the Texas shoreline over 4-5 day period, quite a few taking the storm NE towards LA, the mean keeping Harvey just offshore of the central part of the Texas coast up to day 4.

    IMG_0343.thumb.PNG.a7405e9ebb1044339f4c177d7cf425f0.PNG

    • Like 1

    Hurricane Harvey

    in Hurricanes, Cyclones and Extreme weather worldwide

    Posted · Edited by Nick F

    Seems like it will deepen beyond a cat 1 now, the way updates are evolving Harvey so rapidly it's hard to keep up! What looked like mainly a major/disastrous inland flooding event could also have impacts of damaging winds and devasting storm surge too if it reaches at Cat 3 or worse, as some seem to be now hinting at!

    https://twitter.com/NHC_Atlantic/status/900735336053178370

    https://twitter.com/MJVentrice/status/900735813809471489https://twitter.com/NHC_Atlantic/status/900735336053178370

     

     

    Convective/Storm Discussion Thread - 1st August onwards

    in Storms & Severe Weather

    Posted

    Nice to see reports of thunder and lightning in the SE of England, albeit isolated atm,  was not depicted on my forecast map, I had SW and central S England under general thunderstorm area. But not entirely surprised that mid-level destabilisation of warm moist plume is occurring given highest CAPE has been indicated toward S England but the general consensus from various quarters that the energy will be capped. Goes to show that models are still not great at simulating mid-level convection.

    • Like 3

    Convective/Storm Discussion Thread - 1st August onwards

    in Storms & Severe Weather

    Posted · Edited by Nick F

    Storm & Convective Forecast

    convmap_220817_1.thumb.png.8f26a1e5de956bbc9a3f92e6623e799b.png

    Issued 2017-08-22 06:31:30
    Valid: Tuesday 22 August 6am to Wednesday 23 August 6am

    Day 1 Convective / Storm Forecast

    Synopsis

    Upper and collocated surface low (the weakened remnants of ex-Hurricane Gert) will pull a plume of warm and humid air of sub-tropical origin across the UK, which will destabilise across Ireland/N. Ireland initially then across Scotland and N England Tuesday evening/night.

    … IRELAND, N. IRELAND, SCOTLAND, N ENGLAND and N WALES …

     A plume of warm and humid air advecting north across the British Isles on Tuesday, with wet-bulb potential (WBPT/Theta-w) values reaching 16-18C and characterised by steep lapse rates, will contribute to modest CAPE values reaching 300-700 j/kg ahead of cold front moving in across the far west during the evening and reaching N. Ireland, Wales and SW England early hours of Wednesday.

    This potentially unstable airmass will be capped across much of the UK during Tuesday, however, falling heights and cooling aloft with approach of upper low from the Atlantic combined with divergence in left exit of jet stream, shortwave trough and drier air aloft moving NE across the west will create large scale ascent which will destabilise the plume across Ireland/N Ireland initially in the afternoon … supporting development of heavy showers and thunderstorms, which will then develop or spread northeast across N England then the southern half of Scotland Tuesday evening and overnight into Wednesday morning as forcing moves NE.

    30-40 knots of deep layer shear, strong upper level winds/divergence and linear forcing along/ahead of surface cold front will support organisation of convection/storms into clusters/line segments capable of producing torrential rainfall leading to flash-flooding, strong straight-line winds and hail. Increasing low level shear ahead of cold front and low LCLs (Lifted Condensation Levels or cloud bases) indicated across the west may support an isolated brief tornado too across Ireland, N. Ireland and NW England during diurnal heating cycle before risk drops after dark as surface/boundary layer becomes stable and storms become elevated.

    Have issued a MARGINAL risk, mainly for flooding, across Ireland, N Ireland, far N of Wales, N England and SW Scotland.

    ... SW / CENTRAL S ENGLAND ...

    There is a risk of some elevated heavy showers and thunderstorms across the above areas, mainly this morning before perhaps waning, though risk of isolated thunderstorms along S coastal areas through the day and into the evening as warm moist advection destabilises in mid-levels.

    Issued by: Nick Finnis

    • Like 1

    Model Output Discussions 12z 01/06/2017

    in Forecast Model Discussion

    Posted · Edited by Nick F

    3 hours ago, knocker said:

    As mentioned yesterday it is very difficult to get a handle on the medium term outlook at the moment with so much variability in the system and that includes the anomalies. What, if anything the travels of TS Gert is contributing to this is above my pay grade, but it's very probable that it's having some impact. At the moment in the ten day period we are looking at low pressure in the eastern Arctic with a trough over Greenland and positive anomalies and some amplification of the Azores in the western Atlantic.

    Agree, been watching how ex-Gert interacts and in effect alters the Atlantic jet over last few days and certainly it is still causing some differences between GFS and EC ops and even the GEFS and EPS mean H500 flow as early as day 5-6.

    Day 6 (t+144) GFS and EC H500/SLP ops

    GFS-EC_comp_180817.thumb.JPG.2ba03ee6bbe1c7147569c15a58f08f55.JPG

    Day 6 (t+144) GEFS and EPS H500/SLP mean

    EPS-GEFSH500_comp_180817.thumb.JPG.60b02a3b15ccf770d4a2c111d9912fb4.JPG

    00z GFS wants to track a break-away upper low / surface low with remnants of ex-Gert east across the UK next week, whilst EC keeps the low/ex Gert out west, as the W-E jet weakens, before the low dumbbells around the upper trough over the NW Atlantic and a ridge builds north further east and it warms up quite a bit across the UK next week as a result, especially the south.

    Further along, 00z EC warms things up nicely toward / into last week of August, as another jet streak coming out of N America dives SE and carves out a trough to our west - which draws a plume of warm air north across western/central Europe.

    However, wouldn't have much confidence atm past early next week, given the difference between GFS and ECM!

    • Like 4

    Convective/Storm Discussion Thread - 1st August onwards

    in Storms & Severe Weather

    Posted

    Storm & Convective Forecast

    convmap_180817.thumb.png.4895b133ff5ebfa1f3eb6c22f7c4a721.png

    Issued 2017-08-18 07:38:15
    Valid: 18/08/2017 6am to 19/08/2017 6am

    Day 1 Convective / Storm Forecast

    Synopsis

    Upper trough crosses the UK during Friday, at the surface – parent low moves east to the N of Scotland while one or two surface troughs with associated occluded fronts on the southern side of the low cross the UK and Ireland. An unstable Wly veering NWly flow covers most of the UK, with a risk of thunderstorms developing with diurnal heating.

    … IRELAND, N. IRELAND, ENGLAND, WALES and S SCOTLAND …

    A wedge of rather steep lapse rates over Ireland and far west of UK this morning, associated with cold pool of mid-level air in axis of upper trough moving east, will support the development eastwards of heavy showers / thunderstorms across much of the above areas through the rest of the morning and through the afternoon … as diurnal heating increases surface instability … with GFS indicating 300-700 j/kg across large parts of the UK during peak heating this afternoon away from north Scotland … where cloudier skies and dynamic rainfall will be prevalent.

    Deep layer shear will be fairly weak generally, which will mean showers/storms will be disorganised and pulse-type on the whole. However, across S Ireland, S Wales and S England – stronger Wly flow aloft and 30knts+ of DL shear may organise showers/storms better into clusters/line segments capable of producing marginal risk of strong wind gusts (40-50mph), marginal risk of hail up to 2cm in diameter + marginal risk of flooding. Also, backing of winds / increase in low-level shear ahead of troughs moving through combined with local topographical effects on flow may enhance the risk of an isolated tornado too across S Ireland, Wales and SW England – where LCLs (Lifted Condensation Levels) or cloud bases will be lowest.

     

    Issued by: Nick Finnis

    • Like 1
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