Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260617_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 06/17 12Z 0.24 2009  70  71   9 0.00
Wed 06/17 13Z 0.35 2008  66  60   9 0.00
Wed 06/17 14Z 1.72 2008  62  51   9 0.00
Wed 06/17 15Z 2.93 2108  59  44   9 0.00
Wed 06/17 16Z 2.80 2007  57  30  10 0.00
Wed 06/17 17Z 1.77 1907  56  29  10 0.00
Wed 06/17 18Z 1.73 1808  54  35  11 0.00
Wed 06/17 19Z 1.98 1908  51  54  11 0.00
Wed 06/17 20Z 0.88 1707  52  71  11 0.00
Wed 06/17 21Z 0.29 1708  55  73  11 0.00
Wed 06/17 22Z 0.15 1711  60  82  11 0.00
Wed 06/17 23Z 0.30 1814  65  91  11 0.00
Thu 06/18 00Z 0.38 1816  70  70  11 0.00
Thu 06/18 01Z 0.32 1818  71  35  11 0.00
Thu 06/18 02Z 0.54 1922  76  41  11 0.00
Thu 06/18 03Z 0.55 2023  86  64  10 0.00
Thu 06/18 04Z 0.38 1923  86  64  11 0.01
Thu 06/18 05Z 0.40 2023  88  68  11 0.00
Thu 06/18 06Z 0.45 2122  93  42  11 0.00
Thu 06/18 07Z 0.43 2122  91  69  11 0.00
Thu 06/18 08Z 0.41 2118  90  90  10 0.04
Thu 06/18 09Z 0.14 1817  88  91  11 0.02
Thu 06/18 10Z 0.13 1825  87  95  12 0.00
Thu 06/18 11Z 0.16 1831  84  96  13 0.00
Thu 06/18 12Z 0.19 1836  87  87  14 0.01
Thu 06/18 13Z 0.45 1941  93  93  12 0.03
Thu 06/18 14Z 0.25 1840  81  88  14 0.03
Thu 06/18 15Z 0.33 1838  96  92  13 0.13
Thu 06/18 16Z 0.32 1833  98  78  13 0.23
Thu 06/18 17Z 0.47 1932  98  71  13 0.07
Thu 06/18 18Z 0.58 2030  96  60  14 0.02
Thu 06/18 19Z 0.87 2128  94  54  14 0.00
Thu 06/18 20Z 2.90 2224  88  61  14 0.01
Thu 06/18 21Z 2.93 2424  89  49  13 0.11
Thu 06/18 22Z 1.30 2422  94  55  13 0.01
Thu 06/18 23Z 1.60 2528  92  55  12 0.09
Fri 06/19 00Z 1.56 2527  88  76  11 0.03
Fri 06/19 01Z 1.23 2529  85  62  11 0.01
Fri 06/19 02Z 1.18 2529  85  65  10 0.00
Fri 06/19 03Z 1.01 2629  87  62   9 0.00
Fri 06/19 04Z 0.92 2629  86  63  10 0.00
Fri 06/19 05Z 0.99 2629  89  76   9 0.00
Fri 06/19 06Z 1.04 2630  91  66   8 0.01
Fri 06/19 07Z 1.05 2630  93  64   8 0.01
Fri 06/19 08Z 0.90 2630  93  64   8 0.01
Fri 06/19 09Z 0.86 2631  93  67   9 0.01
Fri 06/19 10Z 0.90 2633  92  62   9 0.01
Fri 06/19 11Z 0.87 2733  92  54   9 0.01
Fri 06/19 12Z 0.89 2733  91  49   9 0.01
Fri 06/19 13Z 0.95 2732  91  39   9 0.01
Fri 06/19 14Z 1.07 2731  90  36   9 0.01
Fri 06/19 15Z 1.44 2729  90  38   9 0.01
Fri 06/19 16Z 2.58 2727  90  45   9 0.00
Fri 06/19 17Z 8.08 2625  89  45   9 0.00
Fri 06/19 18Z 9.28 2623  88  47  10 0.00
Fri 06/19 19Z 10.14 2623  86  40  10 0.00
Fri 06/19 20Z 12.58 2624  84  29  10 0.00
Fri 06/19 21Z 13.72 2625  78  36  10 0.00
Fri 06/19 22Z 13.74 2627  62  25  10 0.00
Fri 06/19 23Z 7.50 2629  68  31  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.95 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1