NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260203_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 02/03 06Z 0.08 3312  63  57  -9 0.00
Tue 02/03 07Z 0.08 3312  64  60  -9 0.00
Tue 02/03 08Z 0.07 3312  63  56  -9 0.00
Tue 02/03 09Z 0.08 3311  62  54  -8 0.00
Tue 02/03 10Z 0.09 3211  61  54  -8 0.00
Tue 02/03 11Z 0.08 3209  61  53  -8 0.00
Tue 02/03 12Z 0.06 3207  60  46  -8 0.00
Tue 02/03 13Z 0.07 3106  60  30  -8 0.00
Tue 02/03 14Z 0.10 2905  61  14  -8 0.00
Tue 02/03 15Z 0.11 2705  63  11  -9 0.00
Tue 02/03 16Z 0.12 2605  66  27  -9 0.00
Tue 02/03 17Z 0.12 2504  71  69  -9 0.00
Tue 02/03 18Z 0.14 2404  71  88 -10 0.00
Tue 02/03 19Z 0.17 2305  67  89 -10 0.00
Tue 02/03 20Z 0.20 2305  59  87 -10 0.00
Tue 02/03 21Z 0.21 2306  55  79 -11 0.00
Tue 02/03 22Z 0.25 2307  55  68 -11 0.00
Tue 02/03 23Z 0.30 2409  63  70 -11 0.00
Wed 02/04 00Z 0.34 2510  86  61 -12 0.00
Wed 02/04 01Z 0.37 2511  93  56 -12 0.00
Wed 02/04 02Z 0.40 2612  92  72 -12 0.00
Wed 02/04 03Z 0.47 2614  90  79 -12 0.00
Wed 02/04 04Z 0.62 2616  90  76 -13 0.00
Wed 02/04 05Z 0.67 2617  93  61 -13 0.00
Wed 02/04 06Z 0.69 2617  94  43 -13 0.01
Wed 02/04 07Z 0.67 2718  93  42 -13 0.01
Wed 02/04 08Z 0.70 2818  94  48 -14 0.01
Wed 02/04 09Z 0.61 2716  91  55 -15 0.01
Wed 02/04 10Z 0.62 2716  87  56 -16 0.00
Wed 02/04 11Z 0.45 2714  86  48 -16 0.00
Wed 02/04 12Z 0.28 2914  82  49 -15 0.00
Wed 02/04 13Z 0.17 3216  82  52 -15 0.00
Wed 02/04 14Z 0.16 3218  85  52 -14 0.00
Wed 02/04 15Z 0.20 3219  85  45 -14 0.00
Wed 02/04 16Z 0.24 3219  89  39 -14 0.00
Wed 02/04 17Z 0.27 3218  90  37 -14 0.00
Wed 02/04 18Z 0.30 3117  86  34 -14 0.00
Wed 02/04 19Z 0.32 3114  79  31 -13 0.00
Wed 02/04 20Z 0.39 3013  80  29 -13 0.00
Wed 02/04 21Z 0.44 2914  84  29 -14 0.00
Wed 02/04 22Z 0.50 2915  87  27 -14 0.00
Wed 02/04 23Z 0.49 2916  88  25 -14 0.00
Thu 02/05 00Z 0.39 3016  87  25 -13 0.00
Thu 02/05 01Z 0.30 3015  85  28 -13 0.00
Thu 02/05 02Z 0.24 3013  85  30 -13 0.00
Thu 02/05 03Z 0.19 3112  85  31 -13 0.00
Thu 02/05 04Z 0.17 3111  87  27 -13 0.00
Thu 02/05 05Z 0.19 3011  89  30 -14 0.00
Thu 02/05 06Z 0.21 3011  90  36 -14 0.00
Thu 02/05 07Z 0.23 3012  90  32 -14 0.00
Thu 02/05 08Z 0.26 2912  91  23 -14 0.00
Thu 02/05 09Z 0.30 2913  93  22 -15 0.00
Thu 02/05 10Z 0.33 2915  93  29 -15 0.00
Thu 02/05 11Z 0.34 3016  93  49 -16 0.00
Thu 02/05 12Z 0.36 3118  92  75 -16 0.00
Thu 02/05 13Z 0.40 3120  90  75 -17 0.00
Thu 02/05 14Z 0.49 3119  90  70 -18 0.01
Thu 02/05 15Z 0.58 3118  92  58 -18 0.00
Thu 02/05 16Z 0.75 3116  93  39 -18 0.00
Thu 02/05 17Z 0.80 3116  93  16 -18 0.00

Run total areal avg QPF for the Central_Greens is: 0.05 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