Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261016_0000
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)
=== ===== === ==== ==== === === === ====
Fri 10/16 00Z 0.05 1904  52   4   5 0.00
Fri 10/16 01Z 0.07 1906  50   5   5 0.00
Fri 10/16 02Z 0.08 1909  50   6   5 0.00
Fri 10/16 03Z 0.10 1812  49   5   6 0.00
Fri 10/16 04Z 0.16 1918  54   7   6 0.00
Fri 10/16 05Z 0.21 1922  66  17   5 0.00
Fri 10/16 06Z 0.23 1926  75  37   5 0.00
Fri 10/16 07Z 0.26 1928  79  60   6 0.00
Fri 10/16 08Z 0.24 1831  76  96   6 0.00
Fri 10/16 09Z 0.25 1834  76  99   6 0.00
Fri 10/16 10Z 0.27 1936  93  97   7 0.04
Fri 10/16 11Z 0.35 1939  97  97   7 0.07
Fri 10/16 12Z 0.40 1940  98  98   8 0.10
Fri 10/16 13Z 0.57 2042  98  91   8 0.19
Fri 10/16 14Z 0.62 2142  98  82  10 0.05
Fri 10/16 15Z 0.62 2139  98  88  11 0.04
Fri 10/16 16Z 0.61 2236  98  96  12 0.05
Fri 10/16 17Z 0.61 2333  98  96  13 0.04
Fri 10/16 18Z 0.64 2431  98  89  13 0.05
Fri 10/16 19Z 0.78 2431  97  95  12 0.05
Fri 10/16 20Z 0.80 2529  95  96  12 0.03
Fri 10/16 21Z 0.94 2430  95  93  11 0.07
Fri 10/16 22Z 1.11 2532  96  90  10 0.12
Fri 10/16 23Z 1.16 2630  94  82   9 0.07
Sat 10/17 00Z 0.94 2726  96  76   8 0.08
Sat 10/17 01Z 0.86 2828  97  57   6 0.04
Sat 10/17 02Z 0.57 3029  94  52   3 0.03
Sat 10/17 03Z 0.64 3129  95  40   0 0.01
Sat 10/17 04Z 0.64 3129  96  49  -1 0.01
Sat 10/17 05Z 0.48 3229  95  49  -2 0.01
Sat 10/17 06Z 0.53 3230  96  45  -3 0.01
Sat 10/17 07Z 0.56 3231  97  40  -4 0.01
Sat 10/17 08Z 0.48 3230  97  38  -4 0.01
Sat 10/17 09Z 0.40 3330  96  40  -5 0.01
Sat 10/17 10Z 0.38 3329  94  29  -5 0.01
Sat 10/17 11Z 0.39 3329  94   6  -6 0.01
Sat 10/17 12Z 0.39 3229  93   0  -7 0.00
Sat 10/17 13Z 0.35 3228  92   0  -7 0.00
Sat 10/17 14Z 0.30 3226  88   2  -8 0.00
Sat 10/17 15Z 0.25 3326  77   3  -8 0.00
Sat 10/17 16Z 0.23 3325  69   2  -8 0.00
Sat 10/17 17Z 0.45 3322  67   1  -9 0.00
Sat 10/17 18Z 1.03 3320  67   2  -9 0.00
Sat 10/17 19Z 1.12 3320  64   3  -8 0.00
Sat 10/17 20Z 1.76 3220  61   1  -8 0.00
Sat 10/17 21Z 2.40 3221  64   5  -8 0.00
Sat 10/17 22Z 1.36 3122  62  14  -8 0.00
Sat 10/17 23Z 0.98 3123  58  22  -8 0.00
Sun 10/18 00Z 0.62 3124  53  26  -8 0.00
Sun 10/18 01Z 0.38 3224  43  33  -7 0.00
Sun 10/18 02Z 0.32 3225  38  40  -7 0.00
Sun 10/18 03Z 0.29 3325  37  30  -6 0.00
Sun 10/18 04Z 0.31 3224  41  19  -6 0.00
Sun 10/18 05Z 0.35 3223  50  17  -7 0.00
Sun 10/18 06Z 0.33 3221  56  15  -7 0.00
Sun 10/18 07Z 0.34 3220  59   6  -6 0.00
Sun 10/18 08Z 0.34 3220  59   6  -6 0.00
Sun 10/18 09Z 0.33 3218  56   3  -5 0.00
Sun 10/18 10Z 0.34 3118  53   3  -4 0.00
Sun 10/18 11Z 0.34 3016  49   2  -4 0.00

Run total areal avg QPF for the Central_Greens is: 1.21 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