jgf

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About jgf

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  • Four Letter Airport Code For Weather Obs (Such as KDCA)
    KHPN
  • Location:
    Connecticut
  • Interests
    Offshore Sailing and Racing
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  1. well, i can understand that.., but given that density varies.., two equal values of dPa S^-1 might have completely different actual vertical velocities.. also.., the 850mb surface is itself defined by pressure.., so now we are talking about the rate of change of pressure, on a constant pressure surface... i guess it could be looking, in a lagrangian sense, at the rate of change of pressure for a particle moving through that 850mb surface.., but maybe rather than speculate i will hope that someone clears it up.
  2. in the 850mb and vertical velocity chart.., the units of vertical velocity are dPa s^-1 i googled it, but couldn't find anything - i am very familiar with the Pascal (Pa) as a unit of pressure.., and i am assuming d is for deci ..,but how are pascals per second a unit of velocity?
  3. I often wonder the same thing - were you looking at the unified surface analysis? I think that they put them any where that MSLP contours close - it may however be a contour level that's not plotted besides front's, i also sometimes see many L's plotted in regions with very weak gradients - a relatively flat but undulating surface could have many places where contours close it might also be be a because they see an area of convection on a satellite i think it varies from forecaster to forecaster - some probably put more than others.., although i understand this is becoming automated, so it could be the computer that's doing it sometimes.
  4. if you look on the IBM website for GRAF, they talk a lot about "democratizing" access to good weather forecasts; "IBM Global High-Resolution Atmospheric Forecasting System (IBM GRAF) helps democratize weather forecasts so people, businesses and governments—anywhere—can make better decisions." and here https://newsroom.ibm.com/graf-democratizing-the-worlds-weather-data yet it seems nearly impossible to actually see any of their forecasting products
  5. are any new houses in upstate new york being built with electric heat today? have you looked into the amount of electricity that would be needed to heat all the houses in new england, and compared that with wind and other renewable electricity coming on line? I live near the water - the wind on the water right now.., dec 22, is about 2kts - it's 23degF outside. it's actually fairly common for low wind speeds to be associated with low temperatures.., as a high builds in. it went down to about 20degF overnight is there really any proposal for enough non wind-dependent, non sunlight-dependent, electricity to heat all the houses in new england? 10 years from now, houses in new england will mostly be heated by oil and gas, just as they are today. about the only renewable with a chance of making a dent in home heating over the next 10 years is wood pellets
  6. did NY also place a moratorium on heating houses? i would bet >95% are heated with oil or gas - and i doubt that will change significantly any time in the next decade
  7. interesting - i have seen cloud streets at sea in the trade winds.., but didn't realize it was the same thing here so, a parcel of air must follow a helical path - roughly from NW to SE in the example above, with the surface winds in a herringbone pattern
  8. big difference between ECMWF and GFS for the track of Invest 95 - this is today's 6z GFS and 6z EC forecast for friday nov 2 GFS in blue, EC in black
  9. In this image, you can clearly see the cold front that has passed over the east coast and moved out to sea. you can also see the expected cloud development in the vicinity of the front - lot's of cumulus clouds right behind the front and pretty high tops at the front. I am asking about the clouds that basically are forming right off the coast - they are pretty low, and aligned in a NNW-SSE direction - parallel to the low level winds.., and perpendicular to the cold front when you watch an animation, the clouds are not really moving offshore - rather they are forming right offshore, and getting entrained in the winds. so we have cold air moving over warmer water - why are the low level NNW -SSE clouds forming?
  10. https://codepen.io/mcmcghee/full/GYmZjZ upper right it's stopped but you can still view the last 5 min or so
  11. Sorry if this should be in the 101 forum..., but I guessed this one would be more appropriate... Anyway... The NOAA NHC Tropical Weather Outlook: https://www.nhc.noaa.gov/gtwo.php?basin=atlc&fdays=2 It gives an estimated probability for a "Tropical Disturbance" to develop into a "Cyclone" over the next few days. For example, in the current TWO, the probability of Disturbance #1 becoming a cyclone is 30% over the next 48hrs, and 40% over the next 5 days. This is the one currently between Bermuda and the Bahamas. Disturbance 1 is elsewhere called Invest 98 I have always figured that the % probability refers to the probability of the tropical disturbance becoming a tropical depression (or greater) - is that correct? The lowest level cyclone is a depression, according to most definitions, so this makes the most sense However, I was trying to confirm this, and looked at the product description page for the Tropical Weather Outlook, but I don't see anything more specific for this development % figure. the description says: "The Tropical Weather Outlook discusses significant areas of disturbed weather and their potential for development during the next 5 days, including a categorical forecast of the probability of tropical cyclone formation during the first 48 hours, and during the entire 5-day forecast period. The 48 h and 5-day probabilities of formation for each disturbance are given to the nearest 10% and expressed in terms of one of the following categories: low probability of development (0-30%), medium probability (40-60%), and high probability of development (70-100%)." https://www.nhc.noaa.gov/aboutnhcprod.shtml#TWO
  12. Euro predicted ~3" for me.., but I got ~8"... that's 2.5 X the forecast...
  13. Copied below is today's WPC Tropical Discussion (which is not the same as the Tropical Weather Discussion issued by the NHC..).., and as you can see it is dominated by discussion of a "pre-frontal shear line". I know what "shear" is - i studied mechanics in graduate school - and I have this definition from the AMS: "Shear Line: In meteorology, a line or narrow zone across which there is an abrupt change in the horizontal wind component parallel to this line; a line of maximum horizontal wind shear." and also this from Wikepedia: "Stationary fronts will either dissipate after several days or devolve into shear lines, but can change into a cold or warm front if conditions aloft change causing a driving of one air mass or the other. Stationary fronts are marked on weather maps with alternating red half-circles and blue spikes pointing in opposite directions, indicating no significant movement. When stationary fronts become smaller in scale, degenerating to a narrow zone where wind direction changes over a short distance, they become known as shear lines.[29] If the shear line becomes active with thunderstorms, it may support formation of a tropical storm or a regeneration of the feature back into a stationary front. A shear line is depicted as a line of red dots and dashes.[13]" This shear line is not depicted on any surface analysis or surface forecast that I have seen. They seem to have a pretty good handle on where it is, and where it will be in the future... i have attached a surface analysis below the discussion.., So, I have a few questions: what data or observations, or model results, are they using to determine the existence of a shear line? would it be expressed in surface winds.., or winds higher up.., or both? How can i see it myself? FXCA20 KWBC 261149PMDCA TROPICAL DISCUSSION - INTERNATIONAL DESKSNWS WEATHER PREDICTION CENTER COLLEGE PARK MD648 AM EST FRI JAN 26 2018PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JAN 26/06UTC: BUILDING POLAR RIDGE OVER THE WESTERN ATLANTIC/EASTERN USA ISDRIVING A POLAR FRONT ACROSS BERMUDA-THE BAHAMAS EARLY THISMORNING. THIS TRIGGERED A PREFRONTAL SHEAR LINE THAT IS SURGINGACROSS THE DOMINICAN REPUBLIC. STRONG BOUNDARY LAYER WINDSACCOMPANY THIS FEATURE...WITH SHIP REPORTS NEAR THE TURKS ANDCAICOS SHOWING WINDS OF 25-30KT. THIS IS ENHANCING LOW LEVELMOISTURE CONVERGENCE ALONG THE SHEAR LINE...WITH SATELLITE DERIVEDPWAT ANALYSIS SHOWING MOISTURE POOLING ACROSS NORTHERN HISPANIOLA.HOWEVER...PERSISTENT MID LEVEL RIDGE AND ASSOCIATED TRADE WINDSCAP CONTINUES TO INHIBIT DEEP CONVECTION IN ASSOCIATION WITH THISFEATURE. AHEAD OF THE SHEAR LINE...A FRESH NORTHEASTERLY FLOW ANDA PWAT MINIMA ENVELOP THE FORECAST AREA.THE SURFACE FRONT IS TO SAG JUST NORTH OF THE FORECAST AREA EARLYON SATURDAY MORNING...WHILE TRAILING ACROSS THE BAHAMAS TO THEFLORIDA PENINSULA. BOUNDARY IS TO REMAIN NEARLY STATIONARY THROUGHEARLY NEXT WEEK...WHEN IT IS EXPECTED TO FRONTOLIZE. THEPREFRONTAL SHEAR LINE MOVES ACROSS THE MONA PASSAGE TO NORTHWESTPUERTO RICO THIS MORNING...PULLING ACROSS SAN JUAN BY 18-21 UTCTODAY. THIS WILL BE ACCOMPANIED BY A 20-30KT WIND SURGE...COLDADVECTION AND A LOW LEVEL CONVERGENT PATTERN. THE SHEAR LINEENTERING THE SAN JUAN METRO AREA WILL COINCIDE WITH PERIOD OF MAXHEATING...ENHANCING CONVECTIVE INSTABILITY AS THIS FEATURE CROSSESTHE ISLAND. THE SHEAR LINE IS THEN FORECAST TO MEANDER BETWEEN THEVIRGIN ISLES-EASTERN PUERTO RICO THROUGH SATURDAY MORNING...MOVINGFARTHER EAST ACROSS THE ISLAND CHAIN LATER IN THE DAY. AS IT PULLSAWAY AND RIDGE STRENGTHENS OVER THE ATLANTIC THE LOW/MID LEVELWINDS ARE TO GRADUALLY VEER TO THE EAST DURING THE WEEKEND. STRONGBOUNDARY LAYER WINDS ARE TO PERSIST THROUGH MONDAY...TO CONTINUEFAVORING A COOL ADVECTIVE PATTERN AND GENERATION OF TRADE WINDSHOWERS ACROSS THE VIRGIN ISLES INTO PUERTO RICO.UNDER THE INFLUENCE OF THE WIND SURGE/SHEAR LINE CONVERGENCE ANDASSOCIATED COLD ADVECTIVE PATTERN...EXPECTING A MORE SEASONALPATTERN OF TRADE WIND SHOWERS TO AFFECT PUERTO RICO AND THE VIRGINISLES DURING THE NEXT FEW DAYS. FURTHERMORE... THE STRONGEREASTERLY TRADES ARE TO ALSO FAVOR GENERATION OF STREAMERS THAT ARETO CONVERGE ACROSS VIEQUES...CULEBRA AND EASTERN PORTIONS OFPUERTO RICO. THESE WILL COMBINE WITH PERSISTENT COOL ADVECTIVEPATTERN AND MEANDERING SHEAR LINE TO LIKELY FAVOR MODERATE TOHEAVY RAINFALL AMOUNTS ACROSS THE VIRGIN ISLES AND EASTERN PUERTORICO/SAN JUAN METRO AREA THIS AFTERNOON THROUGH SATURDAY MORNING.LIGHT TO MODERATE RAINFALL AMOUNTS ARE THEN EXPECTED THROUGHOUTTHE WEEKEND/EARLY NEXT WEEK...WITH MOST ACTIVE CLUSTERING ACROSSTHE EASTERN THIRD OF PUERTO RICO...WITH LOCALIZED MAXIMA OVERSIERRA DE LUQUILLO/EL YUNQUE.DAVISON/GALVEZ...WPC (USA) $$
  14. The SailFlow private sensor on Culebrita survived the passage recording gusts of ~140mph... the sensor is on the light house which is the highest point on the (tiny) island - i've attached a photo i took from the light house a few years ago