NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260416_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)
=== ===== === ==== ==== === === === ====
Thu 04/16 12Z 0.16 2706  87  97  11 0.00
Thu 04/16 13Z 0.19 2507  84  88  11 0.00
Thu 04/16 14Z 0.27 2609  83  74  11 0.00
Thu 04/16 15Z 0.30 2609  83  71  11 0.00
Thu 04/16 16Z 0.31 2408  84  68  11 0.00
Thu 04/16 17Z 0.45 2209  82  71  12 0.00
Thu 04/16 18Z 0.68 2213  83  83  12 0.00
Thu 04/16 19Z 0.86 2215  86  86  13 0.00
Thu 04/16 20Z 0.79 2317  84  70  13 0.00
Thu 04/16 21Z 0.81 2316  83  52  13 0.00
Thu 04/16 22Z 0.65 2316  91  65  13 0.16
Thu 04/16 23Z 0.67 2318  91  26  13 0.07
Fri 04/17 00Z 0.62 2414  88  77  13 0.02
Fri 04/17 01Z 0.49 2916  86  89  11 0.40
Fri 04/17 02Z 0.39 2915  83  96  11 0.12
Fri 04/17 03Z 0.52 2818  92  96  11 0.02
Fri 04/17 04Z 0.61 2820  95  90  10 0.04
Fri 04/17 05Z 0.44 2816  89  85  11 0.02
Fri 04/17 06Z 0.41 2914  92  84  10 0.00
Fri 04/17 07Z 0.37 2914  95  80  10 0.02
Fri 04/17 08Z 0.31 3114  96  94   9 0.03
Fri 04/17 09Z 0.17 3315  96  94   9 0.02
Fri 04/17 10Z 0.07 3415  96  94   9 0.01
Fri 04/17 11Z 0.02 3513  93  85   9 0.01
Fri 04/17 12Z 0.03 3511  93  77   9 0.00
Fri 04/17 13Z 0.03 3511  91  72   9 0.00
Fri 04/17 14Z 0.05 3512  87  67   9 0.00
Fri 04/17 15Z 0.07 0012  80  58   9 0.00
Fri 04/17 16Z 0.11 0112  75  51   9 0.00
Fri 04/17 17Z 0.13 0112  69  48   9 0.00
Fri 04/17 18Z 0.17 0113  63  41   9 0.00
Fri 04/17 19Z 0.22 0212  58  30   9 0.00
Fri 04/17 20Z 0.24 0212  56  24   9 0.00
Fri 04/17 21Z 0.25 0212  55  23   9 0.00
Fri 04/17 22Z 0.25 0212  55  22   9 0.00
Fri 04/17 23Z 0.29 0312  53  21   9 0.00
Sat 04/18 00Z 0.30 0412  52  18   9 0.00
Sat 04/18 01Z 0.29 0511  54  19   9 0.00
Sat 04/18 02Z 0.28 0710  56  16   9 0.00
Sat 04/18 03Z 0.25 0909  64  15   9 0.00
Sat 04/18 04Z 0.25 1109  72  12   8 0.00
Sat 04/18 05Z 0.30 1214  83   9   8 0.00
Sat 04/18 06Z 0.32 1216  78   8   8 0.00
Sat 04/18 07Z 0.38 1218  67   7   8 0.00
Sat 04/18 08Z 0.41 1222  64   7   8 0.00
Sat 04/18 09Z 0.34 1322  66   7   9 0.00
Sat 04/18 10Z 0.26 1422  74   9   8 0.00
Sat 04/18 11Z 0.18 1420  80  15   8 0.00
Sat 04/18 12Z 0.16 1418  81  20   8 0.00
Sat 04/18 13Z 0.18 1419  81  21   8 0.01
Sat 04/18 14Z 0.19 1420  85  22   8 0.01
Sat 04/18 15Z 0.21 1421  87  22   8 0.00
Sat 04/18 16Z 0.19 1421  89  25   8 0.00
Sat 04/18 17Z 0.13 1520  89  26   8 0.00
Sat 04/18 18Z 0.14 1521  86  12   9 0.00
Sat 04/18 19Z 0.09 1521  86   4   9 0.00
Sat 04/18 20Z 0.04 1622  84   6  10 0.00
Sat 04/18 21Z 0.03 1724  81   9  10 0.00
Sat 04/18 22Z 0.04 1725  76  10  11 0.00
Sat 04/18 23Z 0.05 1726  71  47  11 0.01

Run total areal avg QPF for the Central_Greens is: 0.97 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