Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260118_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)
=== ===== === ==== ==== === === === ====
Sun 01/18 18Z 0.51 2308  88  74 -10 0.00
Sun 01/18 19Z 0.42 2307  85  83 -10 0.00
Sun 01/18 20Z 0.27 2304  81  84 -10 0.00
Sun 01/18 21Z 0.13 2102  79  85 -10 0.00
Sun 01/18 22Z 0.06 1801  79  88 -10 0.00
Sun 01/18 23Z 0.07 2100  80  87 -10 0.00
Mon 01/19 01Z 0.06 3300  83  92 -10 0.00
Mon 01/19 02Z 0.08 3102  82  88 -10 0.00
Mon 01/19 03Z 0.08 3203  83  82 -10 0.00
Mon 01/19 04Z 0.08 3304  86  82 -10 0.00
Mon 01/19 05Z 0.10 3403  88  80 -11 0.00
Mon 01/19 06Z 0.11 3403  90  71 -11 0.00
Mon 01/19 07Z 0.09 3404  92  43 -12 0.00
Mon 01/19 08Z 0.09 3103  93  43 -12 0.00
Mon 01/19 09Z 0.11 2803  94  38 -12 0.00
Mon 01/19 10Z 0.14 2603  95  34 -12 0.00
Mon 01/19 11Z 0.25 2606  96  32 -13 0.00
Mon 01/19 12Z 0.41 2509  95  35 -13 0.00
Mon 01/19 13Z 0.37 2509  91  39 -13 0.00
Mon 01/19 14Z 0.39 2310  91  53 -13 0.00
Mon 01/19 15Z 0.59 2212  94  76 -13 0.00
Mon 01/19 16Z 0.90 2215  93  84 -13 0.00
Mon 01/19 17Z 1.78 2216  85  75 -14 0.00
Mon 01/19 18Z 3.40 2216  73  73 -14 0.00
Mon 01/19 19Z 4.20 2317  77  77 -14 0.00
Mon 01/19 20Z 3.40 2318  85  84 -14 0.00
Mon 01/19 21Z 1.19 2320  91  85 -13 0.00
Mon 01/19 22Z 3.62 2325  93  78 -14 0.00
Mon 01/19 23Z 1.75 2426  91  72 -14 0.02
Tue 01/20 00Z 1.63 2428  92  65 -14 0.01
Tue 01/20 01Z 2.15 2429  90  65 -14 0.01
Tue 01/20 02Z 3.51 2431  87  58 -15 0.00
Tue 01/20 03Z 7.51 2531  77  63 -16 0.00
Tue 01/20 04Z 5.32 2532  70  54 -17 0.00
Tue 01/20 05Z 2.45 2534  80  62 -17 0.00
Tue 01/20 06Z 1.50 2632  79  59 -17 0.00
Tue 01/20 07Z 1.50 2529  86  50 -17 0.00
Tue 01/20 08Z 1.51 2530  91  56 -18 0.00
Tue 01/20 09Z 1.81 2530  89  47 -18 0.00
Tue 01/20 10Z 3.14 2628  86  37 -19 0.00
Tue 01/20 11Z 2.43 2625  82  35 -19 0.00
Tue 01/20 12Z 1.83 2624  79  35 -20 0.00
Tue 01/20 13Z 1.57 2624  77  40 -20 0.00
Tue 01/20 14Z 2.70 2622  78  44 -21 0.00
Tue 01/20 15Z 8.10 2619  79  53 -21 0.00
Tue 01/20 16Z 10.42 2517  78  72 -21 0.00
Tue 01/20 17Z 9.75 2517  82  72 -21 0.00
Tue 01/20 18Z 10.11 2519  84  69 -21 0.00
Tue 01/20 19Z 11.41 2521  78  68 -20 0.00
Tue 01/20 20Z 14.31 2524  73  71 -20 0.00
Tue 01/20 21Z 11.81 2625  76  68 -21 0.00
Tue 01/20 22Z 6.11 2626  80  53 -21 0.00
Tue 01/20 23Z 3.20 2626  77  34 -21 0.00
Wed 01/21 00Z 3.50 2627  80  37 -21 0.00
Wed 01/21 01Z 2.30 2727  77  42 -21 0.00
Wed 01/21 02Z 1.47 2727  76  47 -21 0.00
Wed 01/21 03Z 1.29 2627  76  44 -21 0.00
Wed 01/21 04Z 1.09 2726  75  47 -21 0.00
Wed 01/21 05Z 0.96 2625  76  44 -21 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