NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260825_0600
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)
=== ===== === ==== ==== === === === ====
Tue 08/25 06Z 0.43 2314  92  97   8 0.00
Tue 08/25 07Z 0.49 2414  92  93   8 0.00
Tue 08/25 08Z 0.45 2514  95  87   9 0.00
Tue 08/25 09Z 0.44 2513  97  89   9 0.01
Tue 08/25 10Z 0.46 2514  97  90   9 0.01
Tue 08/25 11Z 0.46 2416  98  92   9 0.02
Tue 08/25 12Z 0.46 2515  97  85   9 0.02
Tue 08/25 13Z 0.39 2713  95  86   9 0.01
Tue 08/25 14Z 0.35 2812  94  77   9 0.00
Tue 08/25 15Z 0.36 2912  94  69   9 0.00
Tue 08/25 16Z 0.37 3011  96  63   8 0.00
Tue 08/25 17Z 0.35 3009  96  63   8 0.00
Tue 08/25 18Z 0.32 3008  96  70   9 0.03
Tue 08/25 19Z 0.29 3009  95  76   9 0.07
Tue 08/25 20Z 0.26 3111  94  65   9 0.04
Tue 08/25 21Z 0.25 3111  91  58   9 0.00
Tue 08/25 22Z 0.27 3111  91  63   9 0.02
Tue 08/25 23Z 0.24 3112  90  55  10 0.00
Wed 08/26 00Z 0.24 3113  88  62  10 0.01
Wed 08/26 01Z 0.26 3114  86  56  10 0.00
Wed 08/26 02Z 0.23 3214  86  58  10 0.00
Wed 08/26 03Z 0.21 3214  86  58  10 0.01
Wed 08/26 04Z 0.19 3213  85  53  10 0.00
Wed 08/26 05Z 0.16 3212  83  46   9 0.00
Wed 08/26 06Z 0.17 3212  85  43   9 0.00
Wed 08/26 07Z 0.15 3212  84  40  10 0.00
Wed 08/26 08Z 0.10 3312  81  36  10 0.00
Wed 08/26 09Z 0.09 3311  82  35  10 0.00
Wed 08/26 10Z 0.09 3310  84  34  10 0.00
Wed 08/26 11Z 0.11 3209  85  31  10 0.00
Wed 08/26 12Z 0.10 3208  85  29  10 0.01
Wed 08/26 13Z 0.06 3205  84  24  10 0.00
Wed 08/26 14Z 0.07 3104  84  21  10 0.00
Wed 08/26 15Z 0.08 2903  84  20  10 0.00
Wed 08/26 16Z 0.09 2803  83  17  10 0.00
Wed 08/26 17Z 0.10 2703  83  13  11 0.00
Wed 08/26 18Z 0.12 2603  82  10  11 0.00
Wed 08/26 19Z 0.09 2502  81   8  11 0.00
Wed 08/26 20Z 0.08 2302  80   7  11 0.00
Wed 08/26 21Z 0.10 2203  79   7  11 0.00
Wed 08/26 22Z 0.06 2003  78   4  11 0.00
Wed 08/26 23Z 0.04 1804  78   2  11 0.00
Thu 08/27 00Z 0.07 1905  77   2  11 0.00
Thu 08/27 01Z 0.08 1907  74   4  12 0.00
Thu 08/27 02Z 0.11 1908  70  10  12 0.00
Thu 08/27 03Z 0.13 1909  67  13  12 0.00
Thu 08/27 04Z 0.18 2010  64  18  12 0.00
Thu 08/27 05Z 0.27 2112  62  23  12 0.00
Thu 08/27 06Z 0.32 2113  60  22  12 0.00
Thu 08/27 07Z 0.40 2215  71  21  12 0.00
Thu 08/27 08Z 0.49 2218  79  16  11 0.00
Thu 08/27 09Z 0.55 2219  84  14  11 0.00
Thu 08/27 10Z 0.57 2220  87  16  11 0.00
Thu 08/27 11Z 0.50 2120  83  17  11 0.00
Thu 08/27 12Z 0.48 2121  85  19  11 0.00
Thu 08/27 13Z 0.45 2120  85  17  12 0.00
Thu 08/27 14Z 0.48 2120  93  13  12 0.00
Thu 08/27 15Z 0.49 2019  96  16  11 0.00
Thu 08/27 16Z 0.43 2018  96  21  11 0.00
Thu 08/27 17Z 0.46 1918  97  33  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.26 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