NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260805_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)
=== ===== === ==== ==== === === === ====
Wed 08/05 00Z 0.33 2507  74  13  15 0.00
Wed 08/05 01Z 0.37 2509  72  16  15 0.00
Wed 08/05 02Z 0.33 2408  69  18  15 0.00
Wed 08/05 03Z 0.30 2409  68  19  16 0.00
Wed 08/05 04Z 0.26 2409  66  19  16 0.00
Wed 08/05 05Z 0.27 2409  66  19  16 0.00
Wed 08/05 06Z 0.31 2410  68  19  16 0.00
Wed 08/05 07Z 0.31 2510  70  18  16 0.00
Wed 08/05 08Z 0.29 2609  69  15  16 0.00
Wed 08/05 09Z 0.28 2709  68  14  15 0.00
Wed 08/05 10Z 0.27 2608  69  12  15 0.00
Wed 08/05 11Z 0.24 2607  71  11  15 0.00
Wed 08/05 12Z 0.19 2406  72  10  15 0.00
Wed 08/05 13Z 0.18 2306  72   9  15 0.00
Wed 08/05 14Z 0.21 2306  74   9  14 0.00
Wed 08/05 15Z 0.24 2205  78   8  14 0.00
Wed 08/05 16Z 0.39 2205  80   7  14 0.00
Wed 08/05 17Z 0.39 2105  78   6  14 0.00
Wed 08/05 18Z 0.47 2107  76   5  15 0.00
Wed 08/05 19Z 0.50 2208  71   4  15 0.00
Wed 08/05 20Z 0.39 2108  66   5  16 0.00
Wed 08/05 21Z 0.38 2210  65  14  16 0.00
Wed 08/05 22Z 0.33 2210  64  21  16 0.00
Wed 08/05 23Z 0.33 2211  67  34  16 0.00
Thu 08/06 00Z 0.32 2211  68  36  16 0.00
Thu 08/06 01Z 0.36 2311  71  42  16 0.00
Thu 08/06 02Z 0.40 2311  76  52  16 0.00
Thu 08/06 03Z 0.44 2412  77  66  16 0.00
Thu 08/06 04Z 0.46 2313  79  70  15 0.00
Thu 08/06 05Z 0.46 2413  79  68  16 0.00
Thu 08/06 06Z 0.42 2412  81  75  16 0.00
Thu 08/06 07Z 0.39 2412  82  72  16 0.00
Thu 08/06 08Z 0.37 2411  82  65  16 0.00
Thu 08/06 09Z 0.30 2409  82  61  16 0.00
Thu 08/06 10Z 0.24 2408  80  66  16 0.00
Thu 08/06 11Z 0.16 2306  79  65  16 0.00
Thu 08/06 12Z 0.12 2205  78  62  16 0.00
Thu 08/06 13Z 0.10 2105  79  59  16 0.00
Thu 08/06 14Z 0.11 2104  81  56  16 0.00
Thu 08/06 15Z 0.11 2104  84  50  16 0.00
Thu 08/06 16Z 0.13 2104  85  44  16 0.00
Thu 08/06 17Z 0.17 2204  86  37  16 0.00
Thu 08/06 18Z 0.29 2204  86  45  16 0.00
Thu 08/06 19Z 0.41 2405  84  51  17 0.00
Thu 08/06 20Z 0.38 2404  82  53  17 0.00
Thu 08/06 21Z 0.30 2404  81  57  17 0.00
Thu 08/06 22Z 0.25 2404  82  63  17 0.00
Thu 08/06 23Z 0.19 2404  83  67  17 0.00
Fri 08/07 00Z 0.24 2405  85  69  17 0.00
Fri 08/07 01Z 0.25 2307  87  70  17 0.00
Fri 08/07 02Z 0.23 2307  88  74  17 0.00
Fri 08/07 03Z 0.22 2308  90  75  17 0.01
Fri 08/07 04Z 0.28 2309  90  76  17 0.03
Fri 08/07 05Z 0.31 2410  91  74  17 0.02
Fri 08/07 06Z 0.29 2509  90  71  17 0.01
Fri 08/07 07Z 0.29 2608  91  66  17 0.01
Fri 08/07 08Z 0.27 2708  92  65  17 0.01
Fri 08/07 09Z 0.24 2807  94  59  17 0.01
Fri 08/07 10Z 0.17 2805  94  57  17 0.01
Fri 08/07 11Z 0.16 2804  95  68  16 0.01

Run total areal avg QPF for the greens is: 0.12 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