NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260912_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)
=== ===== === ==== ==== === === === ====
Sat 09/12 06Z 0.04 0005  66  18  10 0.00
Sat 09/12 07Z 0.05 0202  65  18  10 0.00
Sat 09/12 08Z 0.05 1102  63  18  11 0.00
Sat 09/12 09Z 0.03 1402  62  19  11 0.00
Sat 09/12 10Z 0.03 1503  61  22  11 0.00
Sat 09/12 11Z 0.02 1604  59  24  11 0.00
Sat 09/12 12Z 0.02 1706  56  24  12 0.00
Sat 09/12 13Z 0.05 1808  56  23  12 0.00
Sat 09/12 14Z 0.13 1912  60  20  12 0.00
Sat 09/12 15Z 0.22 2013  65  15  11 0.00
Sat 09/12 16Z 0.26 2013  67  10  11 0.00
Sat 09/12 17Z 0.38 2013  70  11  11 0.00
Sat 09/12 18Z 0.59 2013  74  15  11 0.00
Sat 09/12 19Z 0.58 2013  74  14  11 0.00
Sat 09/12 20Z 0.50 2013  70  13  12 0.00
Sat 09/12 21Z 0.42 2016  66  11  12 0.00
Sat 09/12 22Z 0.42 2017  64  10  12 0.00
Sat 09/12 23Z 0.46 2117  76   7  12 0.00
Sun 09/13 00Z 0.51 2118  83   7  12 0.00
Sun 09/13 01Z 0.54 2120  84   9  12 0.00
Sun 09/13 02Z 0.49 2121  86   8  12 0.00
Sun 09/13 03Z 0.54 2123  88  54  12 0.00
Sun 09/13 04Z 0.57 2224  92  65  13 0.00
Sun 09/13 05Z 0.61 2226  84  80  13 0.00
Sun 09/13 06Z 0.66 2227  88  76  13 0.00
Sun 09/13 07Z 0.62 2327  94  67  13 0.01
Sun 09/13 08Z 0.59 2326  95  68  14 0.02
Sun 09/13 09Z 0.54 2423  95  70  14 0.01
Sun 09/13 10Z 0.53 2423  95  66  14 0.01
Sun 09/13 11Z 0.55 2424  96  77  14 0.01
Sun 09/13 12Z 0.54 2423  96  85  14 0.04
Sun 09/13 13Z 0.52 2421  96  82  14 0.03
Sun 09/13 14Z 0.49 2321  96  84  14 0.07
Sun 09/13 15Z 0.48 2320  94  48  14 0.04
Sun 09/13 16Z 0.50 2321  93  27  14 0.02
Sun 09/13 17Z 0.48 2319  94  35  14 0.02
Sun 09/13 18Z 0.45 2318  95  46  14 0.01
Sun 09/13 19Z 0.43 2317  94  52  14 0.01
Sun 09/13 20Z 0.40 2316  93  54  14 0.00
Sun 09/13 21Z 0.38 2314  91  56  15 0.00
Sun 09/13 22Z 0.38 2314  90  52  15 0.00
Sun 09/13 23Z 0.34 2214  90  53  15 0.00
Mon 09/14 00Z 0.42 2315  92  57  14 0.00
Mon 09/14 01Z 0.50 2517  94  62  14 0.00
Mon 09/14 02Z 0.56 2419  95  71  14 0.02
Mon 09/14 03Z 0.64 2421  95  75  14 0.10
Mon 09/14 04Z 0.64 2520  96  84  13 0.06
Mon 09/14 05Z 0.63 2720  93  87  12 0.06
Mon 09/14 06Z 0.43 2917  81  81  13 0.02
Mon 09/14 07Z 0.53 2918  87  83  11 0.00
Mon 09/14 08Z 0.66 2919  90  84  10 0.02
Mon 09/14 09Z 0.75 3021  94  62   9 0.01
Mon 09/14 10Z 0.71 3023  94  53   8 0.01
Mon 09/14 11Z 0.51 3124  94  41   7 0.01
Mon 09/14 12Z 0.44 3125  88  18   6 0.01
Mon 09/14 13Z 0.41 3226  87   6   6 0.00
Mon 09/14 14Z 0.38 3224  88   7   5 0.00
Mon 09/14 15Z 0.32 3322  91   8   5 0.01
Mon 09/14 16Z 0.28 3321  90  11   5 0.00
Mon 09/14 17Z 0.37 3321  88  12   4 0.01

Run total areal avg QPF for the Central_Greens is: 0.64 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