Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261027_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)
=== ===== === ==== ==== === === === ====
Tue 10/27 18Z 0.13 3209  67   5  -1 0.00
Tue 10/27 19Z 0.12 3211  62   4   0 0.00
Tue 10/27 20Z 0.09 3310  56   3   0 0.00
Tue 10/27 21Z 0.12 3211  50   4   0 0.00
Tue 10/27 22Z 0.14 3213  50   4   0 0.00
Tue 10/27 23Z 0.12 3214  52   5   0 0.00
Wed 10/28 00Z 0.12 3212  53   5   0 0.00
Wed 10/28 01Z 0.11 3211  52   5   0 0.00
Wed 10/28 02Z 0.09 3211  48   5   1 0.00
Wed 10/28 03Z 0.08 3210  43   4   1 0.00
Wed 10/28 04Z 0.08 3209  38   4   1 0.00
Wed 10/28 05Z 0.07 3207  32   4   1 0.00
Wed 10/28 06Z 0.07 3106  28   5   2 0.00
Wed 10/28 07Z 0.08 3005  25   7   2 0.00
Wed 10/28 08Z 0.10 2805  24  13   2 0.00
Wed 10/28 09Z 0.11 2605  24  28   2 0.00
Wed 10/28 10Z 0.12 2506  24  60   2 0.00
Wed 10/28 11Z 0.15 2507  25  78   2 0.00
Wed 10/28 12Z 0.18 2508  27  74   3 0.00
Wed 10/28 13Z 0.24 2511  33  70   2 0.00
Wed 10/28 14Z 0.25 2512  36  84   3 0.00
Wed 10/28 15Z 0.26 2613  37  85   3 0.00
Wed 10/28 16Z 0.26 2613  37  82   4 0.00
Wed 10/28 17Z 0.25 2612  37  77   4 0.00
Wed 10/28 18Z 0.24 2711  36  74   5 0.00
Wed 10/28 19Z 0.23 2610  36  71   5 0.00
Wed 10/28 20Z 0.24 2611  37  75   6 0.00
Wed 10/28 21Z 0.25 2611  39  75   6 0.00
Wed 10/28 22Z 0.27 2612  38  68   7 0.00
Wed 10/28 23Z 0.30 2614  45  71   7 0.00
Thu 10/29 00Z 0.31 2614  55  76   8 0.00
Thu 10/29 01Z 0.33 2515  57  71   8 0.00
Thu 10/29 02Z 0.35 2516  63  56   8 0.00
Thu 10/29 03Z 0.37 2516  67  49   8 0.00
Thu 10/29 04Z 0.36 2516  73  38   8 0.00
Thu 10/29 05Z 0.38 2417  74  31   8 0.00
Thu 10/29 06Z 0.41 2419  76  32   8 0.00
Thu 10/29 07Z 0.44 2420  79  31   8 0.00
Thu 10/29 08Z 0.46 2420  83  30   7 0.01
Thu 10/29 09Z 0.49 2521  91  29   7 0.01
Thu 10/29 10Z 0.52 2521  93  28   7 0.02
Thu 10/29 11Z 0.55 2522  93  33   6 0.02
Thu 10/29 12Z 0.56 2621  93  38   6 0.01
Thu 10/29 13Z 0.57 2621  93  49   6 0.01
Thu 10/29 14Z 0.60 2522  93  44   6 0.01
Thu 10/29 15Z 0.62 2523  91  44   6 0.01
Thu 10/29 16Z 0.64 2523  90  38   6 0.00
Thu 10/29 17Z 0.66 2424  88  41   7 0.00
Thu 10/29 18Z 0.66 2424  90  56   7 0.00
Thu 10/29 19Z 0.67 2425  89  47   7 0.00
Thu 10/29 20Z 0.65 2525  86  26   8 0.00
Thu 10/29 21Z 0.72 2528  88  30   8 0.01
Thu 10/29 22Z 0.71 2528  86  28   9 0.01
Thu 10/29 23Z 0.69 2529  84  41   9 0.01
Fri 10/30 00Z 0.67 2530  81  72  10 0.01
Fri 10/30 01Z 0.74 2533  83  87  10 0.01
Fri 10/30 02Z 0.83 2536  86  93   9 0.01
Fri 10/30 03Z 0.90 2537  92  87   9 0.02
Fri 10/30 04Z 0.91 2637  96  80   8 0.02
Fri 10/30 05Z 0.87 2635  97  70   8 0.03

Run total areal avg QPF for the Central_Greens is: 0.23 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