NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260827_0600
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 06Z 0.15 1913  80  20  11 0.00
Thu 08/27 07Z 0.23 1914  78  20  11 0.00
Thu 08/27 08Z 0.32 2017  76  22  11 0.00
Thu 08/27 09Z 0.39 2019  74  21  12 0.00
Thu 08/27 10Z 0.37 2021  72  23  12 0.00
Thu 08/27 11Z 0.37 2022  65  30  12 0.00
Thu 08/27 12Z 0.44 2023  61  31  12 0.00
Thu 08/27 13Z 0.46 2024  61  36  13 0.00
Thu 08/27 14Z 0.48 2124  67  41  13 0.00
Thu 08/27 15Z 0.50 2023  71  43  13 0.00
Thu 08/27 16Z 1.22 2022  78  38  13 0.00
Thu 08/27 17Z 1.32 2021  83  58  13 0.00
Thu 08/27 18Z 0.68 1921  90  84  13 0.01
Thu 08/27 19Z 0.43 2022  91  90  13 0.01
Thu 08/27 20Z 0.34 1921  92  89  14 0.00
Thu 08/27 21Z 0.33 1922  94  85  14 0.03
Thu 08/27 22Z 0.23 1924  95  79  14 0.04
Thu 08/27 23Z 0.39 2025  91  81  14 0.28
Fri 08/28 00Z 0.46 2127  90  79  13 0.19
Fri 08/28 01Z 0.51 2127  92  74  14 0.02
Fri 08/28 02Z 0.55 2226  83  69  14 0.03
Fri 08/28 03Z 0.61 2325  84  71  14 0.02
Fri 08/28 04Z 0.64 2325  88  63  13 0.01
Fri 08/28 05Z 0.64 2424  88  61  14 0.01
Fri 08/28 06Z 0.64 2522  91  56  13 0.01
Fri 08/28 07Z 0.57 2519  92  51  13 0.01
Fri 08/28 08Z 0.48 2616  91  54  13 0.01
Fri 08/28 09Z 0.40 2614  90  46  12 0.01
Fri 08/28 10Z 0.36 2612  90  52  12 0.01
Fri 08/28 11Z 0.32 2611  90  46  12 0.00
Fri 08/28 12Z 0.32 2611  90  41  12 0.00
Fri 08/28 13Z 0.33 2611  91  50  11 0.00
Fri 08/28 14Z 0.31 2610  91  45  11 0.00
Fri 08/28 15Z 0.30 2609  93  40  11 0.00
Fri 08/28 16Z 0.32 2609  93  27  11 0.00
Fri 08/28 17Z 0.35 2609  93  17  11 0.00
Fri 08/28 18Z 0.38 2709  92   8  11 0.00
Fri 08/28 19Z 0.40 2709  94   9  11 0.00
Fri 08/28 20Z 0.37 2810  94   9  11 0.01
Fri 08/28 21Z 0.33 2810  92  10  11 0.00
Fri 08/28 22Z 0.33 2810  93  11  11 0.01
Fri 08/28 23Z 0.31 2910  91  13  10 0.01
Sat 08/29 00Z 0.32 2911  89  15  10 0.00
Sat 08/29 01Z 0.30 3012  86  18  10 0.00
Sat 08/29 02Z 0.27 3012  83  19  10 0.00
Sat 08/29 03Z 0.25 3012  80  19   9 0.00
Sat 08/29 04Z 0.24 3012  74  19   9 0.00
Sat 08/29 05Z 0.23 3012  68  19   9 0.00
Sat 08/29 06Z 0.24 3012  63  15   9 0.00
Sat 08/29 07Z 0.22 3112  56  14   9 0.00
Sat 08/29 08Z 0.22 3112  51  11   9 0.00
Sat 08/29 09Z 0.19 3212  52  12   9 0.00
Sat 08/29 10Z 0.18 3212  52  10   8 0.00
Sat 08/29 11Z 0.16 3211  49   9   8 0.00
Sat 08/29 12Z 0.15 3210  50   7   8 0.00
Sat 08/29 13Z 0.15 3210  52   6   8 0.00
Sat 08/29 14Z 0.17 3109  55   6   8 0.00
Sat 08/29 15Z 0.19 3108  58   6   8 0.00
Sat 08/29 16Z 0.20 3006  60   6   8 0.00
Sat 08/29 17Z 0.30 2906  61   5   8 0.00

Run total areal avg QPF for the greens is: 0.73 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