Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260119_0000
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)
=== ===== === ==== ==== === === === ====
Mon 01/19 00Z 0.06 2600  82  82 -10 0.00
Mon 01/19 01Z 0.10 2903  81  90 -10 0.00
Mon 01/19 02Z 0.10 3104  79  89 -10 0.00
Mon 01/19 03Z 0.08 3104  79  90 -10 0.00
Mon 01/19 04Z 0.06 3404  83  92 -11 0.00
Mon 01/19 05Z 0.08 3505  88  92 -11 0.00
Mon 01/19 06Z 0.08 3505  93  93 -12 0.00
Mon 01/19 07Z 0.08 3403  95  91 -12 0.00
Mon 01/19 08Z 0.08 3102  95  89 -12 0.00
Mon 01/19 09Z 0.11 2702  94  87 -12 0.00
Mon 01/19 10Z 0.11 2603  94  78 -12 0.00
Mon 01/19 11Z 0.24 2506  94  78 -13 0.00
Mon 01/19 12Z 0.34 2508  93  63 -13 0.01
Mon 01/19 13Z 0.33 2408  91  42 -13 0.00
Mon 01/19 14Z 0.34 2309  92  43 -13 0.00
Mon 01/19 15Z 0.47 2211  91  67 -13 0.00
Mon 01/19 16Z 0.96 2214  89  85 -14 0.00
Mon 01/19 17Z 2.24 2215  78  71 -14 0.00
Mon 01/19 18Z 1.71 2315  71  67 -14 0.00
Mon 01/19 19Z 2.24 2315  74  71 -14 0.00
Mon 01/19 20Z 4.31 2217  79  76 -14 0.00
Mon 01/19 21Z 1.79 2220  85  73 -14 0.00
Mon 01/19 22Z 1.35 2324  93  55 -14 0.01
Mon 01/19 23Z 2.13 2326  92  46 -14 0.01
Tue 01/20 00Z 1.95 2428  91  36 -14 0.00
Tue 01/20 01Z 1.75 2427  81  42 -14 0.00
Tue 01/20 02Z 1.71 2329  86  69 -14 0.00
Tue 01/20 03Z 9.70 2531  87  66 -16 0.01
Tue 01/20 04Z 4.52 2530  78  50 -17 0.00
Tue 01/20 05Z 1.72 2432  75  54 -17 0.00
Tue 01/20 06Z 1.80 2534  82  57 -17 0.00
Tue 01/20 07Z 1.51 2533  84  57 -17 0.00
Tue 01/20 08Z 1.66 2532  86  56 -18 0.00
Tue 01/20 09Z 1.38 2530  82  47 -18 0.00
Tue 01/20 10Z 1.43 2530  82  35 -19 0.00
Tue 01/20 11Z 1.62 2628  84  33 -19 0.00
Tue 01/20 12Z 1.60 2625  84  36 -20 0.00
Tue 01/20 13Z 1.68 2624  85  39 -20 0.00
Tue 01/20 14Z 5.26 2623  84  45 -21 0.00
Tue 01/20 15Z 7.52 2620  83  56 -21 0.00
Tue 01/20 16Z 11.38 2619  83  71 -21 0.00
Tue 01/20 17Z 12.02 2519  81  72 -21 0.00
Tue 01/20 18Z 11.21 2519  80  69 -21 0.00
Tue 01/20 19Z 11.56 2520  77  68 -20 0.00
Tue 01/20 20Z 13.64 2623  72  67 -21 0.00
Tue 01/20 21Z 9.34 2623  75  64 -21 0.00
Tue 01/20 22Z 6.42 2625  76  43 -21 0.00
Tue 01/20 23Z 3.90 2626  79  42 -21 0.00
Wed 01/21 00Z 5.32 2628  79  44 -21 0.00
Wed 01/21 01Z 1.74 2728  74  47 -21 0.00
Wed 01/21 03Z 1.23 2628  76  46 -20 0.00
Wed 01/21 04Z 1.13 2628  77  47 -20 0.00
Wed 01/21 05Z 1.06 2628  80  43 -20 0.00
Wed 01/21 06Z 0.99 2628  85  49 -20 0.00
Wed 01/21 07Z 0.89 2627  86  37 -19 0.00
Wed 01/21 08Z 0.81 2527  84  19 -19 0.00
Wed 01/21 09Z 0.81 2528  82  10 -18 0.00
Wed 01/21 10Z 0.78 2529  76  15 -18 0.00
Wed 01/21 11Z 0.69 2527  71  25 -17 0.00

Run total areal avg QPF for the Central_Greens is: 0.04 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