NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260212_1800
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)
=== ===== === ==== ==== === === === ====
Thu 02/12 18Z 1.38 3216  90  54 -13 0.00
Thu 02/12 19Z 0.85 3219  89  38 -13 0.00
Thu 02/12 20Z 0.52 3221  89  23 -12 0.00
Thu 02/12 21Z 0.45 3221  90  17 -12 0.00
Thu 02/12 22Z 0.32 3223  86  17 -12 0.00
Thu 02/12 23Z 0.20 3323  80  14 -11 0.00
Fri 02/13 00Z 0.12 3323  74  11 -10 0.00
Fri 02/13 01Z 0.05 3422  70  10 -10 0.00
Fri 02/13 02Z 0.03 3422  69  11 -10 0.00
Fri 02/13 03Z 0.03 3421  68  11  -9 0.00
Fri 02/13 04Z 0.03 3420  67  12  -9 0.00
Fri 02/13 05Z 0.03 3420  66  12  -9 0.00
Fri 02/13 06Z 0.03 3419  63  13  -9 0.00
Fri 02/13 08Z 0.05 3419  60  15  -9 0.00
Fri 02/13 09Z 0.08 3319  61  18  -9 0.00
Fri 02/13 10Z 0.10 3319  62  23  -9 0.00
Fri 02/13 11Z 0.13 3320  61  27  -9 0.00
Fri 02/13 13Z 0.15 3218  63  26 -10 0.00
Fri 02/13 14Z 0.16 3217  63  25  -9 0.00
Fri 02/13 15Z 0.20 3116  65  22 -10 0.00
Fri 02/13 16Z 0.25 3016  66  21 -10 0.00
Fri 02/13 17Z 0.27 3015  64  19 -10 0.00
Fri 02/13 18Z 0.28 3014  60  19 -10 0.00
Fri 02/13 20Z 0.33 2913  59  19 -10 0.00
Fri 02/13 21Z 0.39 2814  66  23 -10 0.00
Fri 02/13 23Z 0.48 2717  69  51 -10 0.00
Sat 02/14 00Z 0.46 2717  65  40 -10 0.00
Sat 02/14 01Z 0.39 2716  56  41  -9 0.00
Sat 02/14 02Z 0.38 2717  50  45  -9 0.00
Sat 02/14 03Z 0.34 2716  46  53  -8 0.00
Sat 02/14 04Z 0.34 2716  51  63  -8 0.00
Sat 02/14 05Z 0.32 2716  54  63  -8 0.00
Sat 02/14 06Z 0.32 2715  56  85  -8 0.00
Sat 02/14 07Z 0.31 2614  77  81  -9 0.00
Sat 02/14 08Z 0.32 2714  91  83  -9 0.00
Sat 02/14 09Z 0.30 2713  93  81  -9 0.00
Sat 02/14 10Z 0.28 2813  92  80  -9 0.00
Sat 02/14 11Z 0.27 2813  92  81  -9 0.00
Sat 02/14 12Z 0.29 2915  92  81 -10 0.00
Sat 02/14 13Z 0.33 3017  92  82 -10 0.00
Sat 02/14 14Z 0.35 3018  93  67 -10 0.00
Sat 02/14 15Z 0.32 3119  91  34 -10 0.00
Sat 02/14 16Z 0.29 3118  87  17  -9 0.00
Sat 02/14 17Z 0.32 3117  84  17  -9 0.00
Sat 02/14 18Z 0.42 3016  81  21 -10 0.00
Sat 02/14 19Z 0.58 2917  82  24 -10 0.00
Sat 02/14 21Z 0.69 2818  83  25 -10 0.00
Sat 02/14 22Z 0.73 2820  80  24 -10 0.00
Sat 02/14 23Z 0.65 2922  71  22 -10 0.00
Sun 02/15 00Z 0.59 2923  64  25 -10 0.00
Sun 02/15 01Z 0.54 3024  56  26 -10 0.00
Sun 02/15 02Z 0.52 3024  52  33 -10 0.00
Sun 02/15 03Z 0.51 3024  55  39 -11 0.00
Sun 02/15 04Z 0.54 3025  62  44 -11 0.00
Sun 02/15 05Z 0.69 3026  73  48 -12 0.00

Run total areal avg QPF for the Central_Greens is: 0.00 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