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Possible Stormy Spell 13th to 19th Nov

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Author Topic: Possible Stormy Spell 13th to 19th Nov  (Read 3443 times)
martinastro
Martin Mc Kenna
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« on: November 12, 2009, 08:26:48 pm »

19Z Update

A Potent shortwave upper trough visible on WV imagery and Airmass Imagery lies across Ireland into the SW Approaches, the northern filament of this trough and its assoc PVA has engaged the cold front and developed a cyclonic circulation NW of Malin Head.  This is producing quite strong winds in the circulation, gusts to over 40knts and an active rainband moving east.  The cold front is exhibiting strong Line convection elements with hourly totals confiming the NAE's estimates of up to 10mm in an hour or so across many places as the front comes east.  Some very lively echoes across the South and SE need watching for possible embedded convection this evening with Severe Weather diagnostics indicating a possibility of Tornado's and/or strong convective gusts - more esp a little later as the shortwave moves over the front.  Front is currently waving over SW England with more dynamic rain here for a time, however the back edge of this wave likely to turn very convective later this evening as it moves east with gusts to 50knts + possible in places esp around the South Coast headlands.  Thunderstorms, Hail and Weak Isolated Tornadoes possible. Another 10-20mm possible across the South and SW.  Flood Watches will increase dramatically over the next 24 hrs.

To the SW a very strong Jet stream is located North of the Azores. Models have responded to Midday Aireps which suggested this Jet was 5 knts or so stronger and is now analysed at over 165Knts for the next 24hrs before weakening slightly.  At the same time a active upper trough is sharpening and moving east close to 30W.  Over the next 12hrs the shortwave will engage the frontal zone and a deep elongated low will develop. Initially heavy rain will move NE along the warm front giving a lot more rain across the SW, 75mm is possible over the Moors and Mountains in S Wales perhaps locally more. 

The development of the low tomorrow and tomorrow night has become less diverse in the model solutions with most solutions now forming a deep low SSW of Ireland and moving NE, The NAE produces the deepest centre around 958mbs at T+33 SW of Valentia, and then tracks it NE.  The UKMO and ECMWF are similar in moving a deep low NE close to the ISle of Man as a relaxing low but with a deep pressure gradient to the SOuth, essentially the message from all the major guidance is in agreement on the theme.  The detail is a little elusive with risk of Storm Force winds across the SW Coasts rated at 50% at this time IMO.  Gusts in the unstable air give 70mph + in a few places 50-60mmph inland. These gusts close to 925mb winds which in the cold air momentum could drag the stronger winds down esp in showers. 

The cold front also giving strong winds with a zone of Severe Gales likely ahead of the cold front turning into a squally affair.

At this time the UKMO GM and ECM are probably best guidance, the NAE is over deep at the beginning and then relaxes the centre N little too quickly. The GFS also looks to relax the low a quicker than the ECM/UKMO Mix.

More Trouble early next week with another low coming NE, GFS further NW with this ECM/UKMO a little further SOuth, UKMO rather a different solution confining any strong winds to England. ECM a good compromise between UKMO and GFS at this stage.

its hard to keep up at the moment, there is a lot going on.


-----

Paul Blight
UKww Manager - Education/Warnings
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