Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260626_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)
=== ===== === ==== ==== === === === ====
Fri 06/26 00Z 0.53 2213  77  91  10 0.00
Fri 06/26 01Z 0.42 2212  75  93  10 0.00
Fri 06/26 02Z 0.27 2012  75  97  10 0.01
Fri 06/26 03Z 0.11 1813  81  99  10 0.01
Fri 06/26 04Z 0.12 1716  84  99  10 0.02
Fri 06/26 05Z 0.11 1718  89  97  10 0.05
Fri 06/26 06Z 0.09 1721  93  96  10 0.11
Fri 06/26 07Z 0.08 1723  94  97  10 0.11
Fri 06/26 08Z 0.08 1723  90  94  10 0.06
Fri 06/26 09Z 0.09 1825  92  92  10 0.05
Fri 06/26 10Z 0.06 1822  92  86  10 0.01
Fri 06/26 11Z 0.16 1919  94  85  10 0.00
Fri 06/26 12Z 0.22 2018  95  75  10 0.00
Fri 06/26 13Z 0.24 2016  96  75  10 0.01
Fri 06/26 14Z 0.26 2115  97  68  10 0.01
Fri 06/26 15Z 0.31 2213  98  70  10 0.01
Fri 06/26 16Z 0.34 2212  98  67  10 0.01
Fri 06/26 17Z 0.38 2312  96  60  11 0.05
Fri 06/26 18Z 0.40 2309  95  58  11 0.07
Fri 06/26 19Z 0.47 2308  93  67  11 0.07
Fri 06/26 20Z 0.83 2309  93  84  11 0.16
Fri 06/26 21Z 0.65 2611  90  83  11 0.19
Fri 06/26 22Z 0.43 3014  87  81  11 0.11
Fri 06/26 23Z 0.32 3113  86  67  11 0.03
Sat 06/27 00Z 0.36 3011  89  64  11 0.00
Sat 06/27 01Z 0.40 2912  92  52  11 0.00
Sat 06/27 02Z 0.40 2913  93  49  11 0.01
Sat 06/27 03Z 0.36 3012  93  48  10 0.01
Sat 06/27 04Z 0.30 3011  93  44  10 0.01
Sat 06/27 05Z 0.29 3112  92  44  10 0.01
Sat 06/27 06Z 0.24 3211  91  48  10 0.01
Sat 06/27 07Z 0.19 3211  89  55  10 0.01
Sat 06/27 08Z 0.16 3210  87  53  10 0.01
Sat 06/27 09Z 0.16 3210  86  57  10 0.00
Sat 06/27 10Z 0.18 3210  85  55  10 0.00
Sat 06/27 11Z 0.18 3210  85  52  10 0.00
Sat 06/27 12Z 0.17 3210  85  49  10 0.00
Sat 06/27 13Z 0.18 3211  86  47  10 0.00
Sat 06/27 14Z 0.18 3209  88  43  10 0.00
Sat 06/27 15Z 0.18 3207  90  43  10 0.00
Sat 06/27 16Z 0.19 3206  88  42  10 0.00
Sat 06/27 17Z 0.32 3105  87  42  10 0.00
Sat 06/27 18Z 0.33 3104  86  45  11 0.01
Sat 06/27 19Z 0.35 3104  84  46  11 0.01
Sat 06/27 20Z 0.33 3204  82  45  11 0.01
Sat 06/27 21Z 0.12 3302  80  44  11 0.00
Sat 06/27 22Z 0.08 3202  81  48  11 0.01
Sat 06/27 23Z 0.09 3203  80  55  11 0.01
Sun 06/28 00Z 0.04 3403  79  57  12 0.01
Sun 06/28 01Z 0.04 3503  78  58  11 0.01
Sun 06/28 02Z 0.04 3403  77  57  12 0.00
Sun 06/28 03Z 0.04 3403  77  56  11 0.00
Sun 06/28 04Z 0.04 3503  79  54  11 0.00
Sun 06/28 05Z 0.05 3403  79  52  11 0.00
Sun 06/28 06Z 0.04 3403  79  50  11 0.00
Sun 06/28 07Z 0.04 3303  78  49  11 0.00
Sun 06/28 08Z 0.07 3203  78  49  11 0.00
Sun 06/28 09Z 0.06 3305  77  47  11 0.00
Sun 06/28 10Z 0.04 3406  76  44  11 0.00
Sun 06/28 11Z 0.04 3406  75  43  11 0.00

Run total areal avg QPF for the greens is: 1.29 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