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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. 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
  2. jgf

    2018 Atlantic Hurricane Season

    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
  3. jgf

    2018 Atlantic Hurricane Season

    does anyone have any thoughts about this?
  4. 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?
  5. jgf

    Major Hurricane Michael

    https://codepen.io/mcmcghee/full/GYmZjZ upper right it's stopped but you can still view the last 5 min or so
  6. 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
  7. jgf

    Snow bomb obs March 21

    Euro predicted ~3" for me.., but I got ~8"... that's 2.5 X the forecast...
  8. 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) $$
  9. jgf

    Hurricane Maria

    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
  10. jgf

    Major Hurricane Irma

    12Z GFS with WaveWatch III significant wave height in meters 18m - probably the biggest i have ever seen it forecast...
  11. jgf

    Major Hurricane Irma

    Significant Wave Height forecast (meters) from the NOAA WaveWatch III model almost 14m in the center... OPC is saying 50ft possible
  12. jgf

    Major Hurricane Irma

    The School in L'Orient.., would be pretty low (pun intended..) on my list of places to shelter from a hurricane passing just north of the island... i can't really think off hand of any large public buildings that are at high elevation, but many houses/villas are i guess i would probably go to this party and hope for the best! edit - for those who don't know.., even though it says "Guadeloupe".., it is in Gustavia, St. barth, so just a few miles south of the track- St barth is in the french department of guadeloupe, which includes all the french islands in the caribbean
  13. jgf

    Major Hurricane Irma

    i travel there pretty regularly too - while i agree with what you say, i think they will fare better than any other island would if it got hit with a cat 5 eyewall - as they might... it is basically a 1st world place - people don't live in shacks...
  14. jgf

    Can't do Calc: What are my options?

    my very first post in the thread addressed the issue of insufficient proficiency in algebra yes, of course it's critical to have a good working knowledge of algebra before taking even a basic calculus class what i said in that post was that you need to go back to whatever level your weakness starts at, and learn from there - that might even be pre-algebra stuff - fractions, decimals, geometry, and so on... if you do that - and it might take a year or two - i am confident that you can reach a level of preparation that will enable you to succeed in basic calculus class based on your previous posts, i am sure you won't agree, so let's agree to disagree
  15. jgf

    Can't do Calc: What are my options?

    I went to undergraduate school at a pretty good "highly competitive", but not great, smaller liberal arts college, with quite good science departments and very good engineering departments. like a lot of schools, that school had two tracks for first-year calculus. They had an easier track which was basically one year long - 1 semester of differential calc, and one semester of integral calc. This was the "cookbook" class - it was mostly taken by humanities majors, as well as some science/econ majors who wanted a BA rather than a BS. I maintain that pretty much anyone with high school math through algebra could succeed in this calc sequence - i am not sure it even involved trig. I certainly don't agree that it was necessary to "already know the material" to get say a B. nearly all homework and test questions could be solved by following the steps outlined in the example problems. The other track was much harder (different text books), and consisted of 3 semesters - differential, integral, and multivariable. this was mostly math and engineering students, as well as science/econ majors who wanted a BS. This sequence was not cookbook, and i was challenged by it. in this track, there were proofs, and it was common to see questions on exams that were not exactly like anything in the homework. Because i was an idiot and had no clue what i wanted to do.., i ended up taking both! I will note that I am old enough that I was in college before it was common for students to have had calculus in high school. Today, many students going to "highly competitive" colleges have had some level of calculus in high school. My kid's high school offered two levels of first year calc - roughly equivalent to the levels i outlined above, as well as a pretty advanced multivariable class.., and a linear algebra class. the kids taking multivariable and linear algebra, had all had the harder first year of calc in their junior year of high school!
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