NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260827_0000
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 08/27 00Z 0.15 2204  84  36  12 0.00
Thu 08/27 01Z 0.16 2105  84  29  12 0.00
Thu 08/27 02Z 0.12 2005  85  20  12 0.00
Thu 08/27 03Z 0.12 2007  86  15  11 0.00
Thu 08/27 04Z 0.10 1909  86  15  11 0.00
Thu 08/27 05Z 0.13 1911  86  15  11 0.00
Thu 08/27 06Z 0.20 1913  86  16  11 0.00
Thu 08/27 07Z 0.24 2014  85  17  11 0.00
Thu 08/27 08Z 0.32 2016  83  18  11 0.00
Thu 08/27 09Z 0.41 2117  84  18  11 0.00
Thu 08/27 10Z 0.45 2118  85  17  11 0.00
Thu 08/27 11Z 0.47 2119  85  15  11 0.00
Thu 08/27 12Z 0.48 2120  86  16  11 0.00
Thu 08/27 13Z 0.46 2120  87  14  11 0.00
Thu 08/27 14Z 0.50 2120  90  19  11 0.00
Thu 08/27 15Z 0.54 2019  92  36  11 0.00
Thu 08/27 16Z 0.45 1919  92  69  12 0.00
Thu 08/27 17Z 0.24 1919  94  65  12 0.00
Thu 08/27 18Z 0.24 1921  95  60  13 0.01
Thu 08/27 19Z 0.33 1921  94  73  13 0.01
Thu 08/27 20Z 0.33 1922  93  71  13 0.00
Thu 08/27 21Z 0.37 2022  94  84  13 0.00
Thu 08/27 22Z 0.37 2022  93  81  14 0.00
Thu 08/27 23Z 0.34 2022  93  78  14 0.00
Fri 08/28 00Z 0.39 2025  93  77  14 0.00
Fri 08/28 01Z 0.43 2028  92  71  14 0.01
Fri 08/28 02Z 0.51 2129  93  64  14 0.09
Fri 08/28 03Z 0.63 2230  93  58  14 0.05
Fri 08/28 04Z 0.61 2227  92  62  14 0.01
Fri 08/28 05Z 0.64 2325  93  68  13 0.01
Fri 08/28 06Z 0.65 2422  90  62  13 0.01
Fri 08/28 07Z 0.65 2420  94  68  13 0.01
Fri 08/28 08Z 0.58 2518  94  65  13 0.01
Fri 08/28 09Z 0.52 2516  93  45  13 0.01
Fri 08/28 10Z 0.48 2615  92  50  12 0.01
Fri 08/28 11Z 0.43 2613  92  43  12 0.00
Fri 08/28 12Z 0.39 2612  92  33  12 0.01
Fri 08/28 13Z 0.33 2710  92  39  12 0.00
Fri 08/28 14Z 0.30 2709  92  47  12 0.00
Fri 08/28 15Z 0.27 2707  91  43  12 0.01
Fri 08/28 16Z 0.27 2707  92  45  11 0.01
Fri 08/28 17Z 0.37 2707  92  29  11 0.00
Fri 08/28 18Z 0.42 2707  93  29  11 0.00
Fri 08/28 19Z 0.39 2707  94  31  11 0.00
Fri 08/28 20Z 0.32 2807  93  20  11 0.00
Fri 08/28 21Z 0.31 2908  92  16  11 0.00
Fri 08/28 22Z 0.28 3009  92  17  11 0.00
Fri 08/28 23Z 0.27 3009  90  15  11 0.00
Sat 08/29 00Z 0.25 3009  88  14  11 0.00
Sat 08/29 01Z 0.25 3110  84  16  10 0.00
Sat 08/29 02Z 0.23 3110  80  19  10 0.00
Sat 08/29 03Z 0.21 3210  78  16  10 0.00
Sat 08/29 04Z 0.20 3210  76  17  10 0.00
Sat 08/29 05Z 0.20 3110  72  17  10 0.00
Sat 08/29 06Z 0.20 3110  69  20  10 0.00
Sat 08/29 07Z 0.21 3110  65  18  10 0.00
Sat 08/29 08Z 0.18 3210  61  18   9 0.00
Sat 08/29 09Z 0.18 3210  57  16   9 0.00
Sat 08/29 10Z 0.18 3210  54  16   9 0.00
Sat 08/29 11Z 0.16 3310  50  16   9 0.00

Run total areal avg QPF for the greens is: 0.27 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